Sorting Tags Leads to 404

When going to WP Admin>Posts>Tags, I can sort them by asc/desc Name/Description/Slug, but not Posts. Trying to sort them by this number gives me a 404 page.

I’ve tried:

– Disabling all plugins
– Enabling the default WP theme
– Tweaking permissions and .htaccess
– Putting cloudflare into development mode

I thought it might be a problem with permalinks, so I changed it from my custom structure of %category%/%postname% to the default structure.

However that gives me:

You don't have permission to access /wp-admin/edit-tags.php on this server.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

Again, the only trouble happens when trying to sort the tags by post, all the other options work fine.
Why could this be?