We are running a site on WP with more than 10,000+ categories and 50,000+ posts. The problem is the backend keeps timing out due to the Categories widget that's on the individual posts.
I believe what's happening is that WordPress is querying the categories from the database when a user tries to edit a specific post. Is there a solution for this out there? I'm guessing paging this categories list would be the most plausible solution but seeing if anyone has encountered the same issue with having so many categories.