Bug: Companions wandering far from Whiterun + Skjör resurrected

Ok, so I encoutered my first serious bug in Skyrim, and wondered what could have caused it. I am already the Harbinger of the companions, which means Skjör has been dead for a long time now. Njada Stone-arm was my follower, and I used fast travel to go somewhere else (will provide name on departure and arrival location if necessary). Both departure and arrival locations were on the far east of the map, so really far from Whiterun.

So I arrived at this place, and my follower was not there. Far in the distance, I saw a mammoth fighting someone. I wanted to check, just in case, and it was actually Aela, Njada, and Skjör fighting the mammoth. Moreover, Skjör was in a dead-like position (eyes closed, arms crossed on chest, standing straight). And, as if it was not enough, he was half in the ground, so only his chest was emerging off the ground, but he was still moving and running after the mammoth anyway (I couldn’t figure if he was Basically, I saw Skjör’s dead torso sliding off the ground.

After that, I lost them, so I tried to fast travel again to get Njada back at my side, but she was not there. And from there, I couldn’t find her back. I load my game and tried again, and the same thing happened (Aela and Skjör the crazy torso, Njada following them). So I loaded a previous game and went to do something else, but now I’m worried it might happen again when I fast travel again to the same area.

Unfortunately, I was not able to talk to Njada after the fight, so I don’t know if she was still my follower or not.

Anyway, do anyone have any idea about why this could happen? Is it frequent for Aela to be met at totally random places in the world? Or for Skjor to behave like this?

Thanks!