Link to the code that reproduces this issue

https://codesandbox.io/p/devbox/flamboyant-darwin-njgn4r

To Reproduce

1. npx create-next-app@latest
2. npm i react@canary react-dom@canary next@canary babel-plugin-react-compiler
3. Enable React Compiler and PPR in next.config.mjs
4. Create loading.tsx file
5. Start dev server & open in browser

Current vs. Expected behavior

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

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 23.5.0: Wed May  1 20:13:18 PDT 2024; root:xnu-10063.121.3~5/RELEASE_ARM64_T6030
  Available memory (MB): 18432
  Available CPU cores: 11
Binaries:
  Node: 22.2.0
  npm: 10.7.0
  Yarn: 1.22.22
  pnpm: N/A
Relevant Packages:
  next: 15.0.0-canary.106 // Latest available version is detected (15.0.0-canary.106).
  eslint-config-next: 14.2.5
  react: 19.0.0-rc-e948a5ac-20240807
  react-dom: 19.0.0-rc-e948a5ac-20240807
  typescript: 5.5.4
Next.js Config:
  output: N/A

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

create-next-app, Partial Prerendering (PPR)

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

next dev (local)

Additional context

No response