I also remember one time I was on my way back from some mission, completely packed full of loot and passed by a ruin that had a bunch of wiedergängers.
I went on to the nearest town, sold what I wanted to sell and went back to the ruin but now it was populated by ancient legonaries and some honor guards.
The trip back there had not taken more than a day. Was kinda weird but I guess the game just rolls a new garrison for a location everytime you enter a certain radius around it.
Well, to be honest that doesn’t happen to me. Once I discover a ruin or whatever, it keeps the same garrison, type and number of enemies. What happens is that if you discover a location, reload the game and discover it again it will have a different garrison. And I believe the loot and equipment of enemies within changes if you reload the game to the autosave and attack it again.
Thanks for the help!