Yesterday an IP user vandalised a page in ruwiki, see [1]. We can see this edit in the "recentchanges" table of Toolforge DB replica: https://quarry.wmflabs.org/query/23027 . Edit with rc_actor=12321013 is vandal edit, edit with rc_actor=4546 is my rollback. You see 2 records for any edit because one of them contains ores=damaging value and another contains ores=goodfaith value.

When I want to know usernames of this users, I request "actor" table with this actor_id. Request select * from actor where actor_id=4546; returns actor_name "MBH", but request select * from actor where actor_id=12321013; returns zero records.

I have a bot in ruwiki, that rollbacks highly likely vandal edits using ORES scores, and since March 6 this bot rolls back only registered users. As far as I can see, an ability to find username of user, who made some edit, was broken on March 6, because when we join recentchanges table with actor one, this returns only records about registered users.

[1]: https://ru.wikipedia.org/w/index.php?title=Летнее_время&action=history