Please note that I can confirm this only for particular horserace quest. I cannot know if any other quest causes this as I didn’t complete the game yet (neither main story nor all sidequests). I’m keeping an eye and will post if I notice another (side)quest triggers the same problem.
But as I posted on Steam forum, it can be saving/loading issue during some quests…
For example, it could be saving then loading the game in the middle of early mainquest where you ride from Rattay to stables - you could notice there are no random encounters during that sequence. Remember that saving/loading during 3 nightingales quest can corrupt that quest.
I’m just speculating here, not saying it’s a definite cause.
But it can definetly not happen during acompanying Hans to hunting spot - I’ve seen random encounter (beggar) sitting by the road during that one.