Issue with triggering the primary not-found.tsx file of the App Router on each refresh.

[mmdrn]

Issue with Global not-found.tsx in Next.js Application Using Both Pages and App Routers

I have a Next.js application that uses both the Pages Router (for legacy pages) and the App Router (for some migrated routes). From my understanding, when both routers exist in a single project, the global not-found.tsx file in the App Router gets used for 404 errors in the Pages Router as well. In other words, when the Pages Router encounters a 404 error, instead of rendering its own 404.tsx file, the not-found.tsx file from the App Router is triggered.

First of all, please correct me if my understanding is wrong.

The Main Issue

After adding a global not-found.tsx file in the App Router and deploying it to production, we noticed via Sentry logs that it was triggered 15,000 times (as shown in the attached image).

My question is: why is this happening? Is this behavior expected in Next.js when using the not-found.tsx file, or could there be something wrong in my application? Why is this file running even when the not-found page is not triggered??

Additional Context

While debugging, I added a console.error statement in the not-found.tsx file. After building and starting the project, I noticed the following:

• The not-found.tsx file gets triggered, and the console.error is logged whenever I refresh pages that are implemented using the App Router.
• The same happens when navigating from a Pages Router path to an App Router path.

Any insights into why this behavior occurs and whether it's normal or an issue with my setup would be greatly appreciated!

The code of the not-found.tsx:

export default function NotFound() {
  console.error('The global not-found page triggered.')
  return 'not found'
}

[mmdrn]

Update: I removed the entire Pages Router directory from the project, but the issue still persists.

[mmdrn]

Update:

I discovered the issue was related to the SSR of the global not-found.tsx file.
It should be CSR instead. I resolved it by adding 'use client' at the top of the file.

[mmdrn]

The issue still exist