PPR causes key prop warning with Parallel Routes

[Marukome0743]

Link to the code that reproduces this issue

https://github.com/Marukome0743/ppr_unique_key_error

To Reproduce

1. Add ppr: "incremental" option to next.config.mjs.
2. Create Slots folder such as @auth.
3. Start the application in development (next dev).
4. The below warning message will appear in console.
   Each child in a list should have a unique "key" prop. See https://react.dev/link/warning-keys for more information.

Current vs. Expected behavior

Current

Each child in a list should have a unique "key" prop. See https://react.dev/link/warning-keys for more information. shows.

Expected

No warnings.

Provide environment information

Operating System:
  Platform: linux
  Arch: x64
  Version: #1 SMP Fri Mar 29 23:14:13 UTC 2024
  Available memory (MB): 15885
  Available CPU cores: 8
Binaries:
  Node: 22.9.0
  npm: 10.8.3
  Yarn: N/A
  pnpm: N/A
Relevant Packages:
  next: 15.0.0-canary.167 // Latest available version is detected (15.0.0-canary.167).
  eslint-config-next: N/A
  react: 19.0.0-rc-5d19e1c8-20240923
  react-dom: 19.0.0-rc-5d19e1c8-20240923
  typescript: 5.3.3
Next.js Config:
  output: N/A

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

Parallel & Intercepting Routes, Partial Prerendering (PPR)

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

next dev (local)

Additional context

I tested my reproduction against different canary releases, and the first one that introduced the warning was 15.0.0-canary.163, since reverting to 15.0.0-canary.162 works.

Note

The last canary release (15.0.0-canary.167) workflow failed.
That causes mismatching @next/swc version error at canary.
Then temporarily check 15.0.0-canary.166 version instead of canary.

[Marukome0743]

Fixed: #70807

[github-actions]

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