I was afking quite some time above my iron farm and when i dropped down to check the loot i got i noticed two wandering traders that have appeared below me. However, for some odd reason, they were going super fast and i could barely catch them. The llamas went along with them, but as the leash broke they started going normal speed. No idea how to reproduce.
The villager disappeared shortly after.
Here is a video of the trader. The other one was at the same speed as i approached him.

https://www.youtube.com/watch?v=dZosEsZrr2M