Playthrough profile: Level 81 Breton (all skills 100), sided with the Empire, siding with Dawnguard
DLC-related actions taken:
-changed appearance
-re-purchased Dragon elder scroll from the College
-played through Dawnguard up until re-entering the vampire castle in order to get the Blood elder scroll

I cannot proceed any farther, as the game thinks I have a follower, but I do not. This has been an issue since I was sent to find the Moth Priest.

I have waited three days, but whoever is following me did not leave my service. I have no idea where this follower may be. I think it may be Uthgerd the Unbroken, as I have had her as a follower and she is no longer in the Bannered Mare (though I did not kill her), but am unsure; she may have even died at some point. At any rate, the game thinks I have a follower who never gets bored or leaves my service.

Is it possible that they've just become invisible?

I'd really like to find a fix to this bug, as it really messes up my main profile, which I've put hours into playing.

Anyone who suggests waiting longer, please go directly to Oblivion, do not pass Go, do not collect 200 septims.

There is a spoiler section. Use it

I looked through the editing buttons, but didn't find one which allowed me to create spoiler tags.