Whenever I try to edit any List and Search Type or Form and Content Type, I get an infinite loading screen with the message "Oops! Try to close the page & re-open it properly." I've been away from the site for quite a bit, so recently did a number of updates, which may have caused this issue.
Given that this happens with any item I try, it seems to be a site-wide issue or something like that. Any ideas where I should be looking for a solution to this?