[Bug] Specific /index route fails to render in Next.js 15.5.2 while other similar routes work correctly

[childrentime]

Link to the code that reproduces this issue

https://github.com/childrentime/index-route-test

To Reproduce

In Next.js 15.5.2, the specific /index route fails to render with a WebSocket/HMR error, while other similar nested routes (like /index1, /index2, etc.) work perfectly fine. This appears to be a specific issue with the /index path rather than a general routing problem.

Create a Next.js 15.5.2 project with Pages Router
Create the following file structure:
pages/
├── index.tsx # Root page (/)
├── index/
│ └── index.tsx # Should serve /index route
└── index1/
└── index.tsx # Serves /index1 route (works fine)
Start the development server with next dev
Navigate to /index1 - ✅ Works correctly
Navigate to /index - ❌ Fails with rendering error

Current vs. Expected behavior

Expected Behavior
The /index route should render the content from pages/index/index.tsx successfully
Should behave identically to other nested routes like /index1
Actual Behavior
Accessing /index results in a rendering failure with the following error:
ot-reloader-pages.js:199:17)
at eval (hot-reloader-pages.js:72:13)
at WebSocket.handleMessage (websocke
The page fails to render and shows a blank screen or error state
Other routes like /index1 work without any issues

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 23.1.0: Mon Oct  9 21:32:52 PDT 2023; root:xnu-10002.41.9~7/RELEASE_ARM64_T8122
  Available memory (MB): 16384
  Available CPU cores: 8
Binaries:
  Node: 20.11.1
  npm: 10.2.4
  Yarn: 1.22.21
  pnpm: 10.15.0
Relevant Packages:
  next: 15.5.2 // Latest available version is detected (15.5.2).
  eslint-config-next: 15.5.2
  react: 19.1.0
  react-dom: 19.1.0
  typescript: 5.9.2
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Pages Router

Which stage(s) are affected? (Select all that apply)

next dev (local)

Additional context

No response

[childrentime]

@laugharn