Rollback links have an empty from query parameter when the top revisions have been revdel'ed for the username. In this case rollback always fails (despite the presence of MediaWiki:Revertpage-nouser) and the performer is redirected to a page with the message MediaWiki:Alreadyrolled/en.

And, this is a separate issue but the redirected page looks ugly because it contains user links like:

• Cannot rollback the last edit of PAGE by (username removed) (talk | contribs)

where User:(username removed) is globally locked. Perhaps we should have a different interface message?

See also: T279030: It should be possible to rollback to an old revision where the editor was revision deleted (when older revision has hidden username)