Pretty major artifact duplication bug it seems in adventure mode if you display a artifact while the artifact is on its pedestal if you wait/do anything that passes time the artifact gets displaced despite still being on its pedestal so theirs a displaced version of the artifact and the pedestal version if it.
Edit would post it to mantis but dont got a account for it yet.
I just encountered something similar. I walked into a keep, and there was an artifact dagger on the floor - picked it up, gave it to the lord. I fast travelled away and came back later - the dagger was on the floor again, but a copy of it was also in the lords possession - when I picked it up, it vanished from his inventory. He also said "last I heard, I had it".
I don't have a mantis account yet either, so I'm gonna post it here because its really major - companions do not attack other things alongside you. I went into a towns dungeon and attacked a criminal - neither of my companions helped, they weren't tagged as allies either - they didn't run either, just stood there.
To confirm it, I made another adventurer and attacked some random soldiers in a mead hall alongside a companion. Same result - the soldiers all attacked me at once, but the companion just stood there.
I would guess this is related to the identity bugs other people have been posting with "unknown creature" stuff.