Yes! I've also experienced this. I didn't want to say anything about it, or research it to see if anyone else has experienced it, because I thought it would eventually have something to do with some quest, but I have just finished the game to full completion, including side quests, and he still says it and it seems to have nothing to do with anything. He mutters menacing stuff seemingly to himself, such as, "Better let me go or you won't like what happens. You're going to regret this. I have friends enough to make you pay." And it's still present as of patch 1.2.2, on 16 June 2021.

I cannot complete the Horn of Ragnar mystery or the Lady of the lake mystery in Glowecestre. Nothing I have tried works. I can complete the mystery quest right up until the point where the NPC is supposed to turn hostile/violent (in both mysteries), and they just do not attack. They just stand there and do nothing. I have seen on Ubisoft forum (but not Reddit) that one or two others have the problem with the Horn of Ragnar. Ubisoft has offered no solution, and other players solutions don't work for me. I have seen on both Reddit and Ubisoft forum that many, many people have the same problem with the Lady of the Lake. Again, Ubisoft offers no solution, and none of the solutions that have worked for other people have worked for me. Does Ubisoft plan on addressing either of these? Thank for any help or advice.

I play AC Valhalla on PS4. I have noticed that, from time to time, there will be what I call a "pop-up quest" which entails avenging a dead player (I believe an NPC Jomsviking). If you have Eivor inspect the body, Eivor will narrate the manner of death, then you will have the option to avenge the dead body for some XP. Anyway, I sometimes use the skill Explosive Corpse, and when an enemy triggers the booby-trap, they are sometimes killed/disintegrated, not just injured. Sometimes, after this occurs, an "Avenge" quest will pop up, and I will accept. I have noticed that sometimes, the green quest sigil appears at the location of a body that has previously been exploded by the afore-mentioned booby-trap, leaving no body to perform a "confirm kill" on. So when this happens, I cannot complete these quests. Anyway, they are side-quests at most, and I can abandon them at any time, but it is a bit annoying, and I was wondering if anyone else has experienced this or brought it to Ubisoft's attention, so I figured I would ask. Thanks!