One time I had to pick up quest item from the enemy corpse. I failed to sneak and the guard standing next to it attacked me despite it was his enemy too, then I loaded - body disappeared and I had to replay 30 minutes again before the start of quest. It was almost at the beginning of me playing, old version. Probably haven’t reported this since I only needed to replay whole quest.
Second time I was replaying, I wasted time and went to Merhojed later, I could not find body of a sick guy, I did quest otherwise, I simply tried to “break game” and do it my way so I can get what I want with little effort. I read this was long time bug and I do not know if they fixed it.
One similar was side quest, Cuman disappeared, later I found him on another place but could not speak to him probably because I triggered one of the main quests or passed Vranik, can not remember. I was told to replay from start, but I forgot about quest till I almost finished the game.