Btw. it does show results in the dropdown, but not when pressing enter or clicking "show more"

Do they get an error page or will it return 0 results?

it just returns 0 results, but there are listed results in the url

Tricky, try and find similarities with the people who can and who can't. Even in the same role they might be set on different subsidiaries (which could then be a sub restriction - if that how your company is set up.) That's just one example but it will be something silly like that

I have now located one thing those who cant, have in common. they have been moved from the deprecated role "full access". not sure how to fix it, since there is nothing wrong with the new role