I have the issue as well. Started a couple of weeks ago or so. My wife plays splitscreen with me (I could make a splitscreen bug entry as well, but the non-following is worse) but when she doesn't, I often still use her Tav because she is The Master of Unlocking.
Anyway, it is probably my fault in a way as I was sneaking to do things I shouldn't - namely to see if I could somehow steal the Moonlight robe off of Isobel while she and Aylin were in my camp - and while sneaking fired an arrow of darkness which led to a cutscene with Aylin. From that point on Tav will be followed by everyone, but Tav will not follow anyone else as leader. I have to either keep her as the main character interacting with everything or I need to toss her in the wardrobe. Kind of frustrating. I have done all the usual things, grouping and ungrouping in different ways, fast traveling as a group with different leaders, fast traveling independently, killing and resurrecting her both ways. Nothing seems to work.
