Intermittent Cold/Warm App Start Traces Missing in React Native SDK v7.12.1

[masinette]

What React Native libraries do you use?

React Navigation

Are you using sentry.io or on-premise?

sentry.io (SaS)

Are you using any other error monitoring solution alongside Sentry?

No

Other Error Monitoring Solution Name

No response

@sentry/react-native SDK Version

7.12.1

How does your development environment look like?

JS Engine: Hermes
Architecture: The logs reference RN New Architecture indicators (TurboModules/Fabric are not explicitly confirmed but Hermes is present)
Build environment: uat (as seen in the session data: "environment": "uat")
Platform: Android (confirmed via the Android-specific logs, NDK paths, and sentry-android references). iOS was also mentioned as affected.
@sentry/react-native: 7.12.1

Sentry.init()

Configs

In App.tsx:

if (!__DEV__) {
Sentry.init({
// Core Configuration
dsn: Config.SENTRY_DSN,
environment: Config.BUILD_ENV,
release: getVersion(),

// Enable tracing for 100% of transactions
tracesSampleRate: 1.0,

// Watchdog termination tracking
enableWatchdogTerminationTracking: true,

enableAppStartTracking: true,
enableNativeFramesTracking: true,
enableStallTracking: true,
enableUserInteractionTracing: true,
// Integrations (includes routing + app start tracking)
integrations: getSentryIntegrations(),

// For app start tracking (cold/warm start)
enableAutoPerformanceTracing: true,

// CPU profiling for performance analysis
profilesSampleRate: 1.0,

// Track user sessions for release health
enableAutoSessionTracking: true,

// Capture native crashes
enableNativeCrashHandling: true,

// Add sentry-trace header to requests
tracePropagationTargets: ['localhost', /^\//],
});
}

Sentry/index.tsx:
———————————

const routingInstrumentation = reactNavigationIntegration({
// TTID: Time to first frame
enableTimeToInitialDisplay: true,
});
const injectNavigation = (
_navigation: NavigationContainerRef<RouteList> | null,
) => {
routingInstrumentation.registerNavigationContainer(_navigation);
};

const getSentryIntegrations = () => {
return [
reactNativeTracingIntegration({
// End transaction after idle period (9s for mobile networks)
idleTimeoutMs: 9000,
}),
routingInstrumentation,
];
};

Steps to Reproduce

1. Configure @sentry/react-native v7.12.1 with tracesSampleRate: 1.0 and enableAppStartTracking: true.
2. Launch the app from a cold start.
3. Observe that app.start.cold / app.start.warm spans are missing from the transaction in the Sentry dashboard.

Expected Result

Cold and warm start spans should be consistently attached to the first navigation transaction.

Actual Result

The following logs appear, but no app.start.cold or app.start.warm span is logged or sent:
[AppStartIntegration] Waiting for initial app start was flush, before updating based on runApplication call. [AppStart] Captured end frames for app start. { frozenFrames: 0, slowFrames: 0, totalFrames: 0 } [AppStart] App start tracking is enabled. App start will be added to the first transaction as a child span.

No [Tracing] Starting 'app.start.cold' span on transaction... log appears. The warning [ReactNativeTracing] Not instrumenting App Start because native returned null. does not appear either.

[linear-code]

RN-538

[antonis]

Thank you for reporting and documenting this issue @masinette 🙇
We are working on a fix with #5833