404 error handler fails on Next.js 14 site

Support
1

I’m hosting a site built with Next.js on Netlify, and using the standard deploy rather than a static export, and the default settings for deploying Next.js. I originally built it with Next 13, but have updated it recently to Next 14, and it has used the app router since the beginning. It’s at https://highperformancelaravel.com/.

Last weekend I noticed an issue raised by Ahrefs on the site. It was checking for the sitemap at https://highperformancelaravel.com/sitemap_index.xml. While this isn’t where the sitemap normally is (I’m using next-sitemap, which places it at /sitemap.xml), it had been returning a proper 404 response. Now it throws a 502 error with the following text:

This function has crashed
An unhandled error in the function code triggered the following message:

Runtime.UnhandledPromiseRejection - Error: Error handling request. See function logs for details.

Stack trace
Runtime.UnhandledPromiseRejection: Error: Error handling request. See function logs for details.
    at process.<anonymous> (file:///var/runtime/index.mjs:1276:17)
    at process.emit (node:events:529:35)
    at emit (node:internal/process/promises:149:20)
    at processPromiseRejections (node:internal/process/promises:283:27)
    at process.processTicksAndRejections (node:internal/process/task_queues:96:32)

The function log returns the following:

Nov 5, 02:30:36 PM: a17ef05a ERROR  Unhandled Promise Rejection 	{"errorType":"Runtime.UnhandledPromiseRejection","errorMessage":"Error: Error handling request. See function logs for details.","reason":{"errorType":"Error","errorMessage":"Error handling request. See function logs for details.","stack":["Error: Error handling request. See function logs for details.","    at Server.<anonymous> (/var/task/.netlify/functions-internal/___netlify-odb-handler/___netlify-odb-handler.js:88:23)"]},"promise":{},"stack":["Runtime.UnhandledPromiseRejection: Error: Error handling request. See function logs for details.","    at process.<anonymous> (file:///var/runtime/index.mjs:1276:17)","    at process.emit (node:events:529:35)","    at emit (node:internal/process/promises:149:20)","    at processPromiseRejections (node:internal/process/promises:283:27)","    at process.processTicksAndRejections (node:internal/process/task_queues:96:32)"]}Nov 5, 02:30:36 PM: Unknown application error occurred
Runtime.UnknownNov 5, 02:30:36 PM: a17ef05a Duration: 358.34 ms	Memory Usage: 35 MB	Nov 5, 02:30:36 PM: INIT_START Runtime Version: nodejs:18.v15	Runtime Version ARN: arn:aws:lambda:us-east-1::runtime:8ed78fdc4678dbafe30d2afe48bcfb27097048de7858a6fbbba5d19fdc3419db

The same happens for any other 404 errors, despite there being a root app/not-found.tsx file that works as expected when running locally

These errors are rather opaque and I can’t see anything helpful. Can anyone suggest how I might resolve this please?

2

Given that Next 13 itself is having several issues on Netlify, I won’t recommend using Next 14 right now.

3

The issue also occurs in Next 13 - downgrading didn’t resolve the issue.

4

Yes, but next 13 is also having issues on our platform. Can you try downgrading one more time please?

5

Unfortunately that isn’t practical as it’s using the app router.

6

Okay, but there’s nothing we can do to solve it right now. You can try waiting till we fix the issues.

7

Hey, you can now opt-in to our new Next.js runtime (v5) which should resolve this, when coupled with Next.js 13.5+.