From the admin, if I delete a user they disappear from the elements table but not from the users table.

Looking through the code I can see UsersService.php has a function deleteUser which calls the deleteElementById from ElementsService.php - but it does not seem to actually remove the user from the main table at all.

The version of craft in use has recently been updated to 2.9.2 following the Craft CMS guide and I've read there maybe FK issues in the database, but the fixes (plugins) seem to only be for Craft 3, and we are unable to upgrade at this time.

Also looked at > Users not being deleted from the craft_users table?

But as this did not have a full answer and is not a fix for the CMS side of things it's not viable.

How can I determine 1) where the issue is, and 2) how to resolve it?