diff --git a/client/src/Providers/ActivePanelContext.tsx b/client/src/Providers/ActivePanelContext.tsx
index 9d6082d4e4..46b2a189b7 100644
--- a/client/src/Providers/ActivePanelContext.tsx
+++ b/client/src/Providers/ActivePanelContext.tsx
@@ -35,3 +35,11 @@ export function useActivePanel() {
   }
   return context;
 }
+
+/** Returns `active` when it matches a known link, otherwise the first link's id. */
+export function resolveActivePanel(active: string, links: { id: string }[]): string {
+  if (links.length > 0 && links.some((l) => l.id === active)) {
+    return active;
+  }
+  return links[0]?.id ?? active;
+}
diff --git a/client/src/Providers/__tests__/ActivePanelContext.spec.tsx b/client/src/Providers/__tests__/ActivePanelContext.spec.tsx
index 6a6059c9b4..0f2f89e8f7 100644
--- a/client/src/Providers/__tests__/ActivePanelContext.spec.tsx
+++ b/client/src/Providers/__tests__/ActivePanelContext.spec.tsx
@@ -1,7 +1,11 @@
 import React from 'react';
 import { render, fireEvent, screen } from '@testing-library/react';
 import '@testing-library/jest-dom/extend-expect';
-import { ActivePanelProvider, useActivePanel } from '~/Providers/ActivePanelContext';
+import {
+  ActivePanelProvider,
+  resolveActivePanel,
+  useActivePanel,
+} from '~/Providers/ActivePanelContext';
 
 const STORAGE_KEY = 'side:active-panel';
 
@@ -58,3 +62,23 @@ describe('ActivePanelContext', () => {
     spy.mockRestore();
   });
 });
+
+describe('resolveActivePanel', () => {
+  const links = [{ id: 'conversations' }, { id: 'prompts' }, { id: 'files' }];
+
+  it('returns active when it matches a link', () => {
+    expect(resolveActivePanel('prompts', links)).toBe('prompts');
+  });
+
+  it('falls back to first link when active does not match', () => {
+    expect(resolveActivePanel('hide-panel', links)).toBe('conversations');
+  });
+
+  it('returns active unchanged when links is empty', () => {
+    expect(resolveActivePanel('agents', [])).toBe('agents');
+  });
+
+  it('falls back to the only link when active is stale', () => {
+    expect(resolveActivePanel('agents', [{ id: 'conversations' }])).toBe('conversations');
+  });
+});
diff --git a/client/src/components/Agents/Marketplace.tsx b/client/src/components/Agents/Marketplace.tsx
index 0c9c9fb4cc..816705a0db 100644
--- a/client/src/components/Agents/Marketplace.tsx
+++ b/client/src/components/Agents/Marketplace.tsx
@@ -7,11 +7,10 @@ import { useDocumentTitle, useHasAccess, useLocalize, TranslationKeys } from '~/
 import { useGetEndpointsQuery, useGetAgentCategoriesQuery } from '~/data-provider';
 import MarketplaceAdminSettings from './MarketplaceAdminSettings';
 import { SidePanelGroup } from '~/components/SidePanel';
-import { NewChat } from '~/components/Nav';
-import { cn } from '~/utils';
 import CategoryTabs from './CategoryTabs';
 import SearchBar from './SearchBar';
 import AgentGrid from './AgentGrid';
+import { cn } from '~/utils';
 
 interface AgentMarketplaceProps {
   className?: string;
@@ -202,12 +201,6 @@ const AgentMarketplace: React.FC<AgentMarketplaceProps> = ({ className = '' }) =
             ref={scrollContainerRef}
             className="scrollbar-gutter-stable relative flex h-full flex-col overflow-y-auto overflow-x-hidden"
           >
-            {/* Simplified header for agents marketplace - only show nav controls when needed */}
-            {!isSmallScreen && (
-              <div className="sticky top-0 z-20 flex items-center justify-between bg-surface-secondary p-2 font-semibold text-text-primary md:h-14">
-                <NewChat className="border border-border-light bg-surface-secondary p-2" />
-              </div>
-            )}
             {/* Hero Section - scrolls away */}
             {!isSmallScreen && (
               <div className="container mx-auto max-w-4xl">
@@ -222,9 +215,7 @@ const AgentMarketplace: React.FC<AgentMarketplaceProps> = ({ className = '' }) =
               </div>
             )}
             {/* Sticky wrapper for search bar and categories */}
-            <div
-              className={cn('sticky z-10 bg-presentation pb-4', isSmallScreen ? 'top-0' : 'top-14')}
-            >
+            <div className="sticky top-0 z-10 bg-presentation pb-4">
               <div className="container mx-auto max-w-4xl px-4">
                 {/* Search bar */}
                 <div className="mx-auto flex max-w-2xl gap-2 pb-6">
diff --git a/client/src/components/Conversations/Conversations.tsx b/client/src/components/Conversations/Conversations.tsx
index fee9e4fa82..7e7eea4812 100644
--- a/client/src/components/Conversations/Conversations.tsx
+++ b/client/src/components/Conversations/Conversations.tsx
@@ -168,6 +168,8 @@ const Conversations: FC<ConversationsProps> = ({
   const convoHeight = isSmallScreen ? 44 : 34;
   const showAgentMarketplace = useShowMarketplace();
 
+  const favoritesContentKeyRef = useRef('');
+
   // Fetch active job IDs for showing generation indicators
   const { data: activeJobsData } = useActiveJobs();
   const activeJobIds = useMemo(
@@ -179,6 +181,8 @@ const Conversations: FC<ConversationsProps> = ({
   const shouldShowFavorites =
     !search.query && (isFavoritesLoading || favorites.length > 0 || showAgentMarketplace);
 
+  favoritesContentKeyRef.current = `${favorites.length}-${showAgentMarketplace ? 1 : 0}-${isFavoritesLoading ? 1 : 0}`;
+
   const filteredConversations = useMemo(
     () => rawConversations.filter(Boolean) as TConversation[],
     [rawConversations],
@@ -226,7 +230,7 @@ const Conversations: FC<ConversationsProps> = ({
             return `unknown-${index}`;
           }
           if (item.type === 'favorites') {
-            return 'favorites';
+            return `favorites-${favoritesContentKeyRef.current}`;
           }
           if (item.type === 'chats-header') {
             return 'chats-header';
@@ -246,7 +250,6 @@ const Conversations: FC<ConversationsProps> = ({
     [convoHeight],
   );
 
-  // Debounced function to clear cache and recompute heights
   const clearFavoritesCache = useCallback(() => {
     if (cache) {
       cache.clear(0, 0);
@@ -256,13 +259,12 @@ const Conversations: FC<ConversationsProps> = ({
     }
   }, [cache, containerRef]);
 
-  // Clear cache when favorites change
   useEffect(() => {
     const frameId = requestAnimationFrame(() => {
       clearFavoritesCache();
     });
     return () => cancelAnimationFrame(frameId);
-  }, [favorites.length, isFavoritesLoading, clearFavoritesCache]);
+  }, [favorites.length, isFavoritesLoading, showAgentMarketplace, clearFavoritesCache]);
 
   const rowRenderer = useCallback(
     ({ index, key, parent, style }) => {
@@ -280,11 +282,7 @@ const Conversations: FC<ConversationsProps> = ({
       if (item.type === 'favorites') {
         return (
           <MeasuredRow key={key} {...rowProps}>
-            <FavoritesList
-              isSmallScreen={isSmallScreen}
-              toggleNav={toggleNav}
-              onHeightChange={clearFavoritesCache}
-            />
+            <FavoritesList isSmallScreen={isSmallScreen} toggleNav={toggleNav} />
           </MeasuredRow>
         );
       }
@@ -333,7 +331,6 @@ const Conversations: FC<ConversationsProps> = ({
       flattenedItems,
       moveToTop,
       toggleNav,
-      clearFavoritesCache,
       isSmallScreen,
       isChatsExpanded,
       setIsChatsExpanded,
diff --git a/client/src/components/Conversations/__tests__/Conversations.test.tsx b/client/src/components/Conversations/__tests__/Conversations.test.tsx
new file mode 100644
index 0000000000..a4f403fb7f
--- /dev/null
+++ b/client/src/components/Conversations/__tests__/Conversations.test.tsx
@@ -0,0 +1,185 @@
+import React, { createRef } from 'react';
+import { render } from '@testing-library/react';
+import '@testing-library/jest-dom';
+import { RecoilRoot } from 'recoil';
+import type { CellMeasurerCache, List } from 'react-virtualized';
+
+let mockCapturedCache: CellMeasurerCache | null = null;
+
+jest.mock('react-virtualized', () => {
+  const actual = jest.requireActual('react-virtualized');
+  return {
+    ...actual,
+    AutoSizer: ({
+      children,
+    }: {
+      children: (size: { width: number; height: number }) => React.ReactNode;
+    }) => children({ width: 300, height: 600 }),
+    CellMeasurer: ({
+      children,
+    }: {
+      children: (opts: { registerChild: () => void }) => React.ReactNode;
+    }) => children({ registerChild: () => {} }),
+    List: ({
+      rowRenderer,
+      rowCount,
+      deferredMeasurementCache,
+    }: {
+      rowRenderer: (opts: {
+        index: number;
+        key: string;
+        style: object;
+        parent: object;
+      }) => React.ReactNode;
+      rowCount: number;
+      deferredMeasurementCache: CellMeasurerCache;
+      [key: string]: unknown;
+    }) => {
+      mockCapturedCache = deferredMeasurementCache;
+      return (
+        <div data-testid="virtual-list" data-row-count={rowCount}>
+          {Array.from({ length: Math.min(rowCount, 10) }, (_, i) =>
+            rowRenderer({ index: i, key: `row-${i}`, style: {}, parent: {} }),
+          )}
+        </div>
+      );
+    },
+  };
+});
+
+jest.mock('~/store', () => {
+  const { atom } = jest.requireActual('recoil');
+  return {
+    __esModule: true,
+    default: {
+      search: atom({ key: 'test-conversations-search', default: { query: '' } }),
+    },
+  };
+});
+
+type FavoriteEntry = { agentId?: string; model?: string; endpoint?: string };
+
+const mockFavoritesState: { favorites: FavoriteEntry[]; isLoading: boolean } = {
+  favorites: [],
+  isLoading: false,
+};
+
+let mockShowMarketplace = true;
+
+jest.mock('~/hooks', () => ({
+  useFavorites: () => mockFavoritesState,
+  useLocalize: () => (key: string) => key,
+  useShowMarketplace: () => mockShowMarketplace,
+  TranslationKeys: {},
+}));
+
+jest.mock('@librechat/client', () => ({
+  Spinner: () => <div data-testid="spinner" />,
+  useMediaQuery: () => false,
+}));
+
+jest.mock('~/data-provider', () => ({
+  useActiveJobs: () => ({ data: undefined }),
+}));
+
+jest.mock('~/utils', () => ({
+  groupConversationsByDate: () => [],
+  cn: (...args: unknown[]) => args.filter(Boolean).join(' '),
+}));
+
+jest.mock('~/components/Nav/Favorites/FavoritesList', () => ({
+  __esModule: true,
+  default: () => <div data-testid="favorites-list" />,
+}));
+
+jest.mock('../Convo', () => ({
+  __esModule: true,
+  default: () => <div data-testid="convo" />,
+}));
+
+import Conversations from '../Conversations';
+
+describe('Conversations – favorites CellMeasurerCache key invalidation', () => {
+  const containerRef = createRef<List>();
+
+  beforeEach(() => {
+    mockCapturedCache = null;
+    mockFavoritesState.favorites = [];
+    mockFavoritesState.isLoading = false;
+    mockShowMarketplace = true;
+  });
+
+  const Wrapper = () => (
+    <RecoilRoot>
+      <Conversations
+        conversations={[]}
+        moveToTop={jest.fn()}
+        toggleNav={jest.fn()}
+        containerRef={containerRef}
+        loadMoreConversations={jest.fn()}
+        isLoading={false}
+        isSearchLoading={false}
+        isChatsExpanded={true}
+        setIsChatsExpanded={jest.fn()}
+      />
+    </RecoilRoot>
+  );
+
+  it('should invalidate the cached favorites height when favorites count changes', () => {
+    const { rerender } = render(<Wrapper />);
+    const cache = mockCapturedCache!;
+    expect(cache).toBeDefined();
+
+    cache.set(0, 0, 300, 48);
+    expect(cache.has(0, 0)).toBe(true);
+    expect(cache.getHeight(0, 0)).toBe(48);
+
+    mockFavoritesState.favorites = [{ model: 'gpt-4', endpoint: 'openAI' }];
+    rerender(<Wrapper />);
+
+    expect(cache.has(0, 0)).toBe(false);
+  });
+
+  it('should invalidate the cached favorites height when loading state transitions', () => {
+    mockFavoritesState.isLoading = true;
+    const { rerender } = render(<Wrapper />);
+    const cache = mockCapturedCache!;
+
+    cache.set(0, 0, 300, 80);
+    expect(cache.has(0, 0)).toBe(true);
+
+    mockFavoritesState.isLoading = false;
+    rerender(<Wrapper />);
+
+    expect(cache.has(0, 0)).toBe(false);
+  });
+
+  it('should invalidate the cached favorites height when marketplace visibility changes', () => {
+    mockFavoritesState.favorites = [{ model: 'gpt-4', endpoint: 'openAI' }];
+    const { rerender } = render(<Wrapper />);
+    const cache = mockCapturedCache!;
+
+    cache.set(0, 0, 300, 48);
+    expect(cache.has(0, 0)).toBe(true);
+
+    mockShowMarketplace = false;
+    rerender(<Wrapper />);
+
+    expect(cache.has(0, 0)).toBe(false);
+  });
+
+  it('should retain the cached favorites height when content state is unchanged', () => {
+    mockFavoritesState.favorites = [{ model: 'gpt-4', endpoint: 'openAI' }];
+    const { rerender } = render(<Wrapper />);
+    const cache = mockCapturedCache!;
+
+    cache.set(0, 0, 300, 88);
+    expect(cache.has(0, 0)).toBe(true);
+    expect(cache.getHeight(0, 0)).toBe(88);
+
+    rerender(<Wrapper />);
+
+    expect(cache.has(0, 0)).toBe(true);
+    expect(cache.getHeight(0, 0)).toBe(88);
+  });
+});
diff --git a/client/src/components/Nav/Favorites/FavoritesList.tsx b/client/src/components/Nav/Favorites/FavoritesList.tsx
index e47e01fb87..934652349f 100644
--- a/client/src/components/Nav/Favorites/FavoritesList.tsx
+++ b/client/src/components/Nav/Favorites/FavoritesList.tsx
@@ -21,6 +21,7 @@ import { useGetEndpointsQuery } from '~/data-provider';
 import FavoriteItem from './FavoriteItem';
 import store from '~/store';
 
+/** Height intentionally matches FavoriteItem (px-3 py-2 + h-5 icon) to keep the CellMeasurerCache valid across the isAgentsLoading transition. */
 const FavoriteItemSkeleton = () => (
   <div className="flex w-full items-center rounded-lg px-3 py-2">
     <Skeleton className="mr-2 h-5 w-5 rounded-full" />
@@ -118,12 +119,9 @@ const DraggableFavoriteItem = ({
 export default function FavoritesList({
   isSmallScreen,
   toggleNav,
-  onHeightChange,
 }: {
   isSmallScreen?: boolean;
   toggleNav?: () => void;
-  /** Callback when the list height might have changed (e.g., agents finished loading) */
-  onHeightChange?: () => void;
 }) {
   const navigate = useNavigate();
   const localize = useLocalize();
@@ -267,12 +265,6 @@ export default function FavoritesList({
     (allAgentIds.length > 0 && agentsMap === undefined) ||
     (missingAgentIds.length > 0 && missingAgentQueries.some((q) => q.isLoading));
 
-  useEffect(() => {
-    if (!isAgentsLoading && onHeightChange) {
-      onHeightChange();
-    }
-  }, [isAgentsLoading, onHeightChange]);
-
   const draggedFavoritesRef = useRef(safeFavorites);
 
   const moveItem = useCallback(
diff --git a/client/src/components/SidePanel/Nav.tsx b/client/src/components/SidePanel/Nav.tsx
index 5db5b3f5bb..903b32f49b 100644
--- a/client/src/components/SidePanel/Nav.tsx
+++ b/client/src/components/SidePanel/Nav.tsx
@@ -1,12 +1,13 @@
 import type { NavLink } from '~/common';
-import { useActivePanel } from '~/Providers';
+import { useActivePanel, resolveActivePanel } from '~/Providers';
 
 export default function Nav({ links }: { links: NavLink[] }) {
   const { active } = useActivePanel();
+  const effectiveActive = resolveActivePanel(active, links);
   return (
     <div className="flex h-full min-h-0 flex-col overflow-y-auto overflow-x-hidden pt-2 text-text-primary">
       {links.map((link) =>
-        link.id === active && link.Component ? <link.Component key={link.id} /> : null,
+        link.id === effectiveActive && link.Component ? <link.Component key={link.id} /> : null,
       )}
     </div>
   );
diff --git a/client/src/components/UnifiedSidebar/ExpandedPanel.tsx b/client/src/components/UnifiedSidebar/ExpandedPanel.tsx
index 79adbf80a7..74b08a6a29 100644
--- a/client/src/components/UnifiedSidebar/ExpandedPanel.tsx
+++ b/client/src/components/UnifiedSidebar/ExpandedPanel.tsx
@@ -5,7 +5,7 @@ import { QueryKeys } from 'librechat-data-provider';
 import { Skeleton, Sidebar, Button, TooltipAnchor, NewChatIcon } from '@librechat/client';
 import type { NavLink } from '~/common';
 import { CLOSE_SIDEBAR_ID } from '~/components/Chat/Menus/OpenSidebar';
-import { useActivePanel } from '~/Providers';
+import { useActivePanel, resolveActivePanel } from '~/Providers';
 import { useLocalize, useNewConvo } from '~/hooks';
 import { clearMessagesCache, cn } from '~/utils';
 import store from '~/store';
@@ -119,6 +119,7 @@ function ExpandedPanel({
 }) {
   const localize = useLocalize();
   const { active, setActive } = useActivePanel();
+  const effectiveActive = resolveActivePanel(active, links);
 
   const toggleLabel = expanded ? 'com_nav_close_sidebar' : 'com_nav_open_sidebar';
   const toggleClick = expanded ? onCollapse : onExpand;
@@ -149,7 +150,7 @@ function ExpandedPanel({
           <NavIconButton
             key={link.id}
             link={link}
-            isActive={link.id === active}
+            isActive={link.id === effectiveActive}
             expanded={expanded ?? true}
             setActive={setActive}
             onExpand={onExpand}