In my Vanilla World updated from last snapshot and created in 1.13 I have encountered a good number of Wandering Traders with their 2 llamas spawned without commands or spawn eggs. After a while I have been near the mob, it starts running very fast continuously changing direction as if it was escaping from an hostile mob even if it is day and there are no other mobs nearby (a part from the llamas that follow the wandering trader).