In my case when i change only hash url using Router.push(localhost:3000/#change) coming from localhost:3000 all stylesheets reload again causing the screen blink and a error in browser console.
Steps to reproduce the behavior, please provide code snippets or a repository:

This appears fixed on the latest canary Next.js version!
@Timer The problem still persist. The repository inside description still show the console error in 9.5.3-canary.22.
Will look again.
Just re-confirmed it does not reproduce. Please see https://hash-problem.vercel.app/.
Please provide a demo and video if you can get it to reproduce for you!
I made some tests using https://hash-problem.vercel.app/ and chrome browser, and the problem in console and the screen blink still persist.
Ps: In Mozilla Firefox doesnt happens.
Please, see the video here.
If you need more details, just ask me for it.
Wow, I can't reproduce that at all. Since you can reproduce do you think you could try to send a PR fixing the unhandled promise rejection?
Sure, but i don't know what the solution is. what do I do?
I tried this myself, and only got issues if I went to Chrome's device mode (as a fake iPhone) and IMMEDIATELY spammed the button; however, I only get the error/flash once.
I can reproduce in Chrome but only with DevTools open and "Disable cache" (Network tab) option enabled.
Can y'all test the latest Next.js canary and see if the flash of styles is fixed for you?
@Timer Fixed!! :clap:
I've test using https://hash-problem.vercel.app/, the repository in description and in my personal private repository.
Thank you for all your support about this.
Gonna close this out then!
Most helpful comment
Can y'all test the latest Next.js canary and see if the flash of styles is fixed for you?