Hi,
welcome to the forum.
I’d guess that a CSS or JS resource is being blocked, maybe one that’s loaded via PHP. If you send me the URL in a PM, I can check what it might be and what you’d need to whitelist.
With HTProtect active, it should be pretty easy to spot 403 - Forbidden errors in the browser console – either in the Console or Network tab.
The info in the shield protection chapter might also help: https://htprotect.org/dokumentation
Cheers
Pascal