I have a unique bug involving Paxton Rall.
On my Plasmatech Vanguard, he did the actual recruitment mission for Paxton Rall, rather than use the token. He got Rall and didn't lose any other companions; however, Darth Hexid is in the "other followers" column and cannot be called forth.
Here's the unique part: I never had Hexid to begin with, since I did not fulfill requirements outlined in the Dark vs Light event.
Additional info, if it helps: this is a toon I took all the way from level 1 and has completed up through Iokath but has not started Umbara and beyond.