Rubio was hard to find under specific play-circumstances. This hotfix should make it so that he always appears in the Desert, but can only be recruited once the Castle questline starts, after the old Demonhunter tower visit. Sorry for the inconvenience.
Oh, and before I get report-assaulted about this :p
If you priorly talked to Rubio without recrutiing him (him disappearing) then saved, then used that save in the hotfix.. its not gonna make him reappear. This is about the end of current content anyway, look forward to the Bimbo Castle release, coming next week.