Hey there @StefanJakubjak! Welcome back to the community! I was strolling by and thought it could be one of two things, and you mentioned them both already. The vehicles have a bool for if they aren’t being rendered they may not operate. In this case for the VehicleMovementComponent it’s this bool:
To check if it’s the AI controller, the Blackboard, or the Actor itself, have some print behind it’s detection logic to see if it still works when you’re away. If the level has world partition and streaming enabled, disabled streaming for a sec and verify if it’s working on another streaming proxy or not.