notFound() thrown in dynamic segment shows "pages" 404 while app/not-found.tsx is present

[MKraust]

Verify canary release

• I verified that the issue exists in the latest Next.js canary release

Provide environment information

Operating System:
      Platform: darwin
      Arch: arm64
      Version: Darwin Kernel Version 22.4.0: Mon Mar  6 20:59:28 PST 2023; root:xnu-8796.101.5~3/RELEASE_ARM64_T6000
    Binaries:
      Node: 18.16.1
      npm: 9.5.1
      Yarn: N/A
      pnpm: 8.3.1
    Relevant Packages:
      next: 13.4.17
      eslint-config-next: 13.4.17
      react: 18.2.0
      react-dom: 18.2.0
      typescript: 5.1.6
    Next.js Config:
      output: N/A

Which area(s) of Next.js are affected? (leave empty if unsure)

App Router, Routing (next/router, next/navigation, next/link)

Link to the code that reproduces this issue or a replay of the bug

https://github.com/MKraust/next-404-segment-bug

To Reproduce

1. Run npm run build && npm run start
2. Go to /dynamic/404
3. See that "pages" 404 is rendered inside app/dynamic/layout.tsx instead of app/not-found.tsx
4. Go to /foo/bar
5. See that app/not-found.tsx is rendered correctly
6. Go to /dynamic-with-not-found/404
7. See that app/dynamic-with-not-found/[slug]/not-found.tsx is rendered correctly (same if move app/dynamic-with-not-found/[slug]/not-found.tsx to app/dynamic-with-not-found/not-found.tsx)

Describe the Bug

notFound() thrown in dynamic segment shows "pages" 404 while root app/not-found.tsx is present.

Expected Behavior

I expect that notFound() thrown anywhere would propagate to the first matching not-found.tsx in the app/ hierarchy.
In case of /dynamic/404 it's root app/not-found.tsx. It's working properly on next@13.4.12

That behavior is described here. Specifically, the words:

Good to know: In addition to catching expected notFound() errors, the root app/not-found.js file also handles any unmatched URLs for your whole application.

Which browser are you using? (if relevant)

115.0.5790.170 (arm64)

How are you deploying your application? (if relevant)

next start

[MKraust]

Could be related to #53703, #54080 and #54051 (specifically, "pages" 404 still used if app/not-found.tsx is present).

[github-actions]

This closed issue has been automatically locked because it had no new activity for 2 weeks. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.