Recently I tried to move a WordPress instance to a production server and (besides other issues) had to deal with a page that could not be deleted via the admin panel. The success message would show up but the entry remains in the list and doesn't get removed. Also the content association with this page was somehow broken. It would always show an empty box when editing but the content that should have been there was showing up on the page.
Now I've came across a undeletable user in another instance that I didn't do anything funky with (like changing it's environment). Same behavior: It gives me the green 'User deleted' message but doesn't actually do anything. I noticed that for this user the Name column is empty, but in the database the
user_nicename value is there. Weird..
I know this is probably very hard to diagnose and answer here, but maybe someone had similar issues in the pasts and gained some insights?