fix: prevent initial send failed live region crash

Author: OEvgeny

CHANGELOG.md

@@ -23,6 +23,10 @@ Legends:
 
 - Added `styleOptions.richCardTitleOmitHeadingRole` (default `false`) to opt out of `style: 'heading'` on rich card titles, in PR [#5839](https://github.com/microsoft/BotFramework-WebChat/pull/5839), by [@cjennison](https://github.com/cjennison)
 
+### Fixed
+
+- Fixed an error when a failed activity is present when Web Chat mounts, resolving [#5812](https://github.com/microsoft/BotFramework-WebChat/issues/5812), by [@OEvgeny](https://github.com/OEvgeny)
+
 
 ## [4.19.1] - 2026-06-09
 

packages/component/src/Transcript/LiveRegion/SendFailed.spec.tsx

@@ -0,0 +1,49 @@
+/** @jest-environment @happy-dom/jest-environment */
+
+import React from 'react';
+import { render } from 'react-dom';
+import { act } from 'react-dom/test-utils';
+
+import { hooks } from 'botframework-webchat-api';
+
+import LiveRegionSendFailed from './SendFailed';
+import { useLiveRegion } from '../../providers/LiveRegionTwin';
+
+jest.mock('botframework-webchat-api', () => ({
+  hooks: {
+    useGetActivityByKey: jest.fn(),
+    useLocalizer: jest.fn(),
+    useSendStatusByActivityKey: jest.fn()
+  }
+}));
+jest.mock('../../providers/LiveRegionTwin', () => ({ useLiveRegion: jest.fn() }));
+
+const mockUseGetActivityByKey = hooks.useGetActivityByKey as jest.Mock;
+const mockUseLiveRegion = useLiveRegion as jest.Mock;
+const mockUseLocalizer = hooks.useLocalizer as jest.Mock;
+const mockUseSendStatusByActivityKey = hooks.useSendStatusByActivityKey as jest.Mock;
+
+describe('LiveRegionSendFailed', () => {
+  let container: HTMLDivElement;
+
+  beforeEach(() => {
+    container = document.createElement('div');
+
+    mockUseGetActivityByKey.mockReturnValue(() => ({ channelData: {}, text: 'Hello, World!', type: 'message' }));
+    mockUseLocalizer.mockReturnValue(() => 'Failed to send message.');
+    mockUseSendStatusByActivityKey.mockReturnValue([new Map([['activity', 'send failed']])]);
+  });
+
+  afterEach(() => {
+    container.remove();
+    jest.clearAllMocks();
+  });
+
+  test('renders when the initial send status is failed', () => {
+    act(() => {
+      render(<LiveRegionSendFailed />, container);
+    });
+
+    expect(mockUseLiveRegion.mock.calls[0][0]()).toBe(false);
+  });
+});

packages/component/src/Transcript/LiveRegion/SendFailed.tsx

@@ -48,7 +48,7 @@ const LiveRegionSendFailed = () => {
 
   /** True, if one or more non-presentational activities start appears as "send failed", otherwise, false. */
   const hasNewSendFailed = useMemo<boolean>(() => {
-    if (activityKeysOfSendFailed === prevActivityKeysOfSendFailed) {
+    if (!prevActivityKeysOfSendFailed || activityKeysOfSendFailed === prevActivityKeysOfSendFailed) {
       return false;
     }