User profile page is not found (404) - emails not showing

[bartv (Bart)]

I’m experiencing the same issue on some old accounts as well: I can access the admin page, but the email field won’t show, and the user profile returns a 404. I have an unconfirmed suspicion that this is somehow caused by usernames that are identical except for an underscore (in my case ‘MissB’ and ‘Miss_B’ - the underscore is a remnant from a vBulletin import). Both accounts had this issue, but on one of them it has since disappeared (the one with the underscore is still having the same problem).