"invalid file path" error ONLY when not logged in

Hi folks,

I migrated a WordPress installation to another server (Windows VM), or let’s say I copied it using a tool that changes all the links in the DB as well.

So now the wordpress installation is running on the 2nd server, but I can’t display the frontend when I’m not logged into the backend.
I always get the error “invalid file path”.
As soon as I am logged in, the page loads without any issues.

Is this known to somebody? The page is public, everything is published and it’s really a 1:1 copy of the productive website on the 1st server.