I was right: he did indeed appear in different places, when I took to long to move somewhere else. He made Oxenfordshire really annoying, because it turned out, that he also took a spot on my horse, meaning I could not place people there to get them to the questmarker. Instead I had walk with them on my shoulders. And just to give you an idea how annoying this became: here he is busy "photobombing" cutscenes (sometimes even making them almost unwatchable because he would stand right in front of the camera).


Luckily I had an older save, so I didn't have to restart the whole game and thinking about it, I believe the glitching happened elsewhere: In the quest "Pilgrimage to St Albanes" I traveled with Basim and Sigurd to Albanes, but teleported to Raventhorpe before completing the mission there. When I went back I couldn't find Sigurd nor Basim anyhwere so I started a Raid and my Raiders killed the monk guarding Faulke before I could trigger the cutscene with him. So I think either me teleporting away and then completing the quest without my allies or my crew killing the monk triggered a not despawning ally.

@ubi-swaggins sure



and here on the right could be the deertrophy, so the game is only displaying one of my trophies (if that's is indeed the trophy)

I killed a few alpha animals and turned their trophies in. The NPC gave me a reward (i.e. a new tattoo something like that) and told me that the trophies would be mounted in the longhouse. Well, they seem to be hidden really well, as I can't find anything on the walls or anywhere else there.

After reaching Lunden I foolishly freed some NPCs in the Fort in Lundens upper westside. Well that was a decision I came to regret now as one of those Raiders keeps following me. I already teleported away, went to Norway and even restarted the game, but as soon as I come back to Lunden, he's appears quickly. And honestly, I think the only thing that kept him away in other places (when I teleported to Raventhorpe for example) is probably just the fact, that I went somewhere else before he could reach me there as well. Captured my stalker in the screenshot below



At least he fights my enemies as well.