dinoframe

This helped. Thank you, Manuel!

Do you guys need any more information from me, so you can check this? Let me know

Same happens to me. The regex stops working.
I did some investigation and found:

Looks like the reason for this is an invisible “Zero-width space” (%E2%80%8B) characters get added to the requested URL somehow.

If I copy a URL from 404 log page and then URL-Encode it, I get these characters in the URL: %E2%80%8B

Of course, the regex would not match those characters.

Thanks, Tom.
Random folder name can be cracked by a brute-force attack. It should not take a lot of attempts.