fix: App hanging when changing passcode on iOS

- Add 300ms delay between authentication and passcode change modals
- Add try-catch to handle authentication cancellation gracefully
- Prevents iOS UI thread hang when two modals open back-to-back

Fixes #6313

Author: DSingh0304

app/lib/constants/localAuthentication.ts

@@ -11,3 +11,6 @@ export const MAX_ATTEMPTS = 6;
 export const TIME_TO_LOCK = 30000;
 
 export const DEFAULT_AUTO_LOCK = 1800;
+
+// Delay between modal transitions to prevent iOS UI thread hang
+export const MODAL_TRANSITION_DELAY_MS = 300;

app/views/ScreenLockConfigView.test.tsx

@@ -0,0 +1,126 @@
+import * as localAuthentication from '../lib/methods/helpers/localAuthentication';
+import { MODAL_TRANSITION_DELAY_MS } from '../lib/constants/localAuthentication';
+
+// Mock the localAuthentication module
+jest.mock('../lib/methods/helpers/localAuthentication', () => ({
+	handleLocalAuthentication: jest.fn(),
+	changePasscode: jest.fn(),
+	checkHasPasscode: jest.fn(),
+	supportedBiometryLabel: jest.fn()
+}));
+
+describe('ScreenLockConfigView - Passcode Change with Modal Delay', () => {
+	beforeEach(() => {
+		jest.clearAllMocks();
+		jest.useFakeTimers();
+	});
+
+	afterEach(() => {
+		jest.useRealTimers();
+	});
+
+	it('should add 300ms delay between authentication and passcode change', async () => {
+		const handleLocalAuthenticationMock = localAuthentication.handleLocalAuthentication as jest.Mock;
+		const changePasscodeMock = localAuthentication.changePasscode as jest.Mock;
+
+		handleLocalAuthenticationMock.mockResolvedValue(undefined);
+		changePasscodeMock.mockResolvedValue(undefined);
+
+		// Simulate the flow: authentication -> delay -> passcode change
+		const simulatePasscodeChange = async (autoLock: boolean) => {
+			if (autoLock) {
+				try {
+					await handleLocalAuthenticationMock(true);
+					// Add delay using the same constant as the component
+					await new Promise(resolve => setTimeout(resolve, MODAL_TRANSITION_DELAY_MS));
+				} catch {
+					return;
+				}
+			}
+			await changePasscodeMock({ force: false });
+		};
+
+		const promise = simulatePasscodeChange(true);
+
+		// Verify handleLocalAuthentication was called
+		await Promise.resolve(); // Flush microtasks
+		expect(handleLocalAuthenticationMock).toHaveBeenCalledWith(true);
+
+		// Fast-forward timers to simulate the 300ms delay
+		jest.runAllTimers();
+
+		await promise;
+
+		// Verify changePasscode was called after the delay
+		expect(changePasscodeMock).toHaveBeenCalledWith({ force: false });
+	});
+
+	it('should handle authentication cancellation gracefully', async () => {
+		const handleLocalAuthenticationMock = localAuthentication.handleLocalAuthentication as jest.Mock;
+		const changePasscodeMock = localAuthentication.changePasscode as jest.Mock;
+
+		// Simulate user canceling authentication
+		handleLocalAuthenticationMock.mockRejectedValue(new Error('Authentication cancelled'));
+
+		// Simulate the flow with error handling
+		const simulatePasscodeChange = async (autoLock: boolean) => {
+			if (autoLock) {
+				try {
+					await handleLocalAuthenticationMock(true);
+					await new Promise(resolve => setTimeout(resolve, MODAL_TRANSITION_DELAY_MS));
+				} catch {
+					// User cancelled - should return early
+					return;
+				}
+			}
+			await changePasscodeMock({ force: false });
+		};
+
+		await simulatePasscodeChange(true);
+
+		// Verify handleLocalAuthentication was called
+		expect(handleLocalAuthenticationMock).toHaveBeenCalledWith(true);
+
+		// Verify that changePasscode was NOT called when authentication fails
+		expect(changePasscodeMock).not.toHaveBeenCalled();
+	});
+
+	it('should proceed directly to passcode change when autoLock is disabled', async () => {
+		const handleLocalAuthenticationMock = localAuthentication.handleLocalAuthentication as jest.Mock;
+		const changePasscodeMock = localAuthentication.changePasscode as jest.Mock;
+
+		changePasscodeMock.mockResolvedValue(undefined);
+
+		// Simulate the flow without authentication
+		const simulatePasscodeChange = async (autoLock: boolean) => {
+			if (autoLock) {
+				try {
+					await handleLocalAuthenticationMock(true);
+					await new Promise(resolve => setTimeout(resolve, MODAL_TRANSITION_DELAY_MS));
+				} catch {
+					return;
+				}
+			}
+			await changePasscodeMock({ force: false });
+		};
+
+		await simulatePasscodeChange(false);
+
+		// Verify handleLocalAuthentication was NOT called
+		expect(handleLocalAuthenticationMock).not.toHaveBeenCalled();
+
+		// Verify changePasscode was called directly
+		expect(changePasscodeMock).toHaveBeenCalledWith({ force: false });
+	});
+
+	it('should use correct delay duration from constant', () => {
+		// Create a promise that resolves after the delay
+		const delayPromise = new Promise(resolve => setTimeout(resolve, MODAL_TRANSITION_DELAY_MS));
+
+		// Advance timers by the constant value
+		jest.advanceTimersByTime(MODAL_TRANSITION_DELAY_MS);
+
+		// The promise should resolve
+		return expect(delayPromise).resolves.toBeUndefined();
+	});
+});

app/views/ScreenLockConfigView.tsx

@@ -12,7 +12,7 @@ import {
 	supportedBiometryLabel,
 	handleLocalAuthentication
 } from '../lib/methods/helpers/localAuthentication';
-import { BIOMETRY_ENABLED_KEY, DEFAULT_AUTO_LOCK } from '../lib/constants/localAuthentication';
+import { BIOMETRY_ENABLED_KEY, DEFAULT_AUTO_LOCK, MODAL_TRANSITION_DELAY_MS } from '../lib/constants/localAuthentication';
 import { themes } from '../lib/constants/colors';
 import SafeAreaView from '../containers/SafeAreaView';
 import { events, logEvent } from '../lib/methods/helpers/log';
@@ -132,7 +132,15 @@ class ScreenLockConfigView extends React.Component<IScreenLockConfigViewProps, I
 	changePasscode = async ({ force }: { force: boolean }) => {
 		const { autoLock } = this.state;
 		if (autoLock) {
-			await handleLocalAuthentication(true);
+			try {
+				await handleLocalAuthentication(true);
+				// Add a small delay to ensure the first modal is fully closed before opening the next one
+				// This prevents the app from hanging on iOS when two modals open back-to-back
+				await new Promise(resolve => setTimeout(resolve, MODAL_TRANSITION_DELAY_MS));
+			} catch {
+				// User cancelled or authentication failed
+				return;
+			}
 		}
 		logEvent(events.SLC_CHANGE_PASSCODE);
 		await changePasscode({ force });

app/views/SecurityPrivacyView.tsx

@@ -6,6 +6,7 @@ import * as List from '../containers/List';
 import SafeAreaView from '../containers/SafeAreaView';
 import I18n from '../i18n';
 import { ANALYTICS_EVENTS_KEY, CRASH_REPORT_KEY } from '../lib/constants/keys';
+import { MODAL_TRANSITION_DELAY_MS } from '../lib/constants/localAuthentication';
 import { useAppSelector } from '../lib/hooks/useAppSelector';
 import useServer from '../lib/methods/useServer';
 import { type SettingsStackParamList } from '../stacks/types';
@@ -59,7 +60,14 @@ const SecurityPrivacyView = ({ navigation }: ISecurityPrivacyViewProps): JSX.Ele
 
 	const navigateToScreenLockConfigView = async () => {
 		if (server?.autoLock) {
-			await handleLocalAuthentication(true);
+			try {
+				await handleLocalAuthentication(true);
+				// Add a small delay to prevent modal conflicts on iOS
+				await new Promise(resolve => setTimeout(resolve, MODAL_TRANSITION_DELAY_MS));
+			} catch {
+				// User cancelled or authentication failed
+				return;
+			}
 		}
 		navigateToScreen('ScreenLockConfigView');
 	};