Random 403s when using Cloudflare workers

For example, Consider this WPT report

I’m using Cloudflare worker for prototyping.

If you check it’s run #2, you’ll see a lot’s of 403s for CSS:

Now if you check the run #4 you will see that those 403s are not there anymore and there are some other requests with 403.

If I check this in browser, I don’t get any 403s and everything works.
why is this happening in WPT and why it’s so random?

How do I go about fixing this?