See rename logs, here some usernames have started showing wiki suffix (@enwiki,@metawik...), only these ones have problems.
For example see this one, it's the first rename with the problem, here the account got renamed to "Саша Попов Александр Алексеевич" but CA shows it doesn't exist, but GRP shows the rename is successfully done.
Same thing with other renames where the rename log is showing wiki suffix for previous username. It says the rename's done but neither user gets renamed nor page moves happen.
First I thought it to be my browser's cache problem but it's same with other browsers. Also checked with alternative account.