Is there any update on this? The rename is stuck for a week so far, while other renames have been going fine. I suppose the user is not able to login at this moment since the rename is not finished.

In T198449#4326334, @matmarex wrote:

The bug has been fixed, but the fix still needs to be deployed to Wikimedia wikis. Usually deployments are not done on Fridays (so that we will not have to call up people on the weekend if anything new breaks). Judging by the number of reports, it definitely seems like a noticeable problem, is this causing major issues for users/administrators, or could you folks live with it until Monday? @greg It might be worth making an exception.

I also found that rollbacks now have both "Rollback" and "Undo" tags applied, instead of just the "Rollback" tag applied previously. e.g. https://meta.wikimedia.org/wiki/Special:Diff/18164356