Sentry.lastEventId() doesn't work on SSR when the error is thrown in the component render #19691

Is there an existing issue for this?

• I have checked for existing issues https://github.com/getsentry/sentry-javascript/issues
• I have reviewed the documentation https://docs.sentry.io/
• I am using the latest SDK release https://github.com/getsentry/sentry-javascript/releases

How do you use Sentry?

Sentry Saas (sentry.io)

Which SDK are you using?

@sentry/nextjs

SDK Version

10.41.0

Framework Version

NextJS v15

Link to Sentry event

No response

Reproduction Example/SDK Setup

// sentry-test.tsx
import React from 'react';

const SentryTest: React.FC = () => {
    throw new Error('This is a test 2 error for Sentry integration.');
};

export default SentryTest;

// _error.tsx
CustomError.getInitialProps = async (pageContext) => {
  const { err, res } = pageContext;
  const statusCode = res?.statusCode || 500;

  // This currently returns undefined
  const lastEventId = await Sentry.captureUnderscoreErrorException(pageContext);

  return { statusCode, lastEventId };
};

Steps to Reproduce

1. Set up a Next.js app using the Pages Router without getServerSideProps
2. Create a page that throws during render or in getInitialProps
3. In _error.tsx, call captureUnderscoreErrorException(pageContext) in getInitialProps
4. Observe that the returned value is always undefined
5. Confirm Sentry.getIsolationScope().lastEventId() returns undefined

Possible Root Cause

Sentry's webpack loader wraps _error.tsx via pageWrapperTemplate.ts, which applies wrapErrorGetInitialPropsWithSentry to the page's getInitialProps. Inside that wrapper, the user's getInitialProps is passed through withErrorInstrumentation before being called.

When an error is thrown during component render or in a page's getInitialProps, withErrorInstrumentation catches it and calls captureException on it — setting __sentry_captured__ = true on the error object. By the time the user's getInitialProps runs and calls captureUnderscoreErrorException, the error is already marked as captured and its isolation scope is already torn down.

captureUnderscoreErrorException then hits this branch:

if (err && core.isAlreadyCaptured(err)) {
  responseEnd.waitUntil(responseEnd.flushSafelyWithTimeout());
  return core.getIsolationScope().lastEventId(); // always undefined — scope is gone
}

This design assumes errors originate from getServerSideProps, where Sentry wraps each function individually and the isolation scope is still active when _error.getInitialProps runs. When errors come from component render or page-level getInitialProps instead, withErrorInstrumentation captures the error at the _error wrapper level first, and the scope is already gone by the time captureUnderscoreErrorException runs.

Current Workaround

Store the event ID in beforeSend and read it from the error object in _error.tsx:

// sentry.server.config.ts
beforeSend(event, hint) {
  const err = hint?.originalException;
  if (err && typeof err === 'object' && event.event_id) {
    (err as any).__sentry_event_id__ = event.event_id;
  }
  return event;
}

// _error.tsx
CustomError.getInitialProps = async (pageContext) => {
  const { err, res } = pageContext;
  const statusCode = res?.statusCode || 500;
  const lastEventId =
    (err as any)?.__sentry_event_id__ ??
    await Sentry.captureUnderscoreErrorException(pageContext);
  return { statusCode, lastEventId };
};

Expected Result

Get the lastEventId in getInitialProps() in _error.tsx when calling Sentry.captureUnderscoreErrorException(pageContext) or Sentry.lastEventId() after the error is captured.

Actual Result

We get undefined.

While debugging in the server, we can see that the _lastEventId value is undefined by the time it reaches getInitialProps.

Additional Context

Even if we don't get the lastEventId, it's correctly being sent to Sentry, so that part is not an issue.

Priority

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