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 22.5.0: Mon Apr 24 20:53:44 PDT 2023; root:xnu-8796.121.2~5/RELEASE_ARM64_T8103
    Binaries:
      Node: 18.15.0
      npm: 9.5.0
      Yarn: 3.5.1
      pnpm: 8.6.1
    Relevant packages:
      next: 13.4.5-canary.9
      eslint-config-next: N/A
      react: 18.2.0
      react-dom: 18.2.0
      typescript: 5.1.3

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

No response

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

https://github.com/danmartens/next-error-repro

To Reproduce

I tried to create as minimal of a reproduction as possible. Instructions are in the repository, but basically you can run pnpm install and then node test.mjs broken to see the reproduction. That script will build the app and then repeatedly visit the broken URL via Puppeteer.

It only happens about 4-6% in the app I'm working on, but I was able to get it to happen basically 100% of the time by playing around with it for a while. The issue seems to be related to some sort of race condition, so you may have to increase the delay value in src/app/broken/test-1/layout.tsx to reproduce the issue. On my machine, I start to see failures with a 3ms delay and the error rate reaches ~100% with a 6ms or greater delay.

Describe the Bug

When an async component that imports CSS renders within an async page component with an adjacent loading.tsx and an async layout component with export const revalidate = 0;, Next will generate invalid script tags for importing the CSS if the request takes longer than a certain amount of time. The script tags look like this and are always the last element before the </body> tag:

<script>B:1","S:1",[["/_next/static/css/ef46db3751d8e999.css","next"]])</script>

Expected Behavior

All <script> tags should contain valid JavaScript.

Which browser are you using? (if relevant)

No response

How are you deploying your application? (if relevant)

No response