Description of the Bug
If I was away from a train(s) with chunkloaders and closed and opened world this often happens (doesnt seem to happen while I'm staying ingame(just away):
Train on turn may get splitted to 2 parts and start move together on parallel tracks. Result video:
https://vimeo.com/483470033
latest.log

Some of this is probably just minecraft's shitty entity handling.

if train came from unrendered area, this may happen (without even reopening world)