I experimented with some minecarts in a private world and released that sometimes the minecarts go through eachother. I have a old world where I use this mechanic for redstone that the minecarts colliade with eachother and and now it only does work sometimes. It doesnˈt matter if an entity is in the minecart or not it can be better reproduced if there is some lag in the world.

A video with the reproduction of the bug: https://1drv.ms/v/s!AknKLCEsl1RcguYnQq71-QYxtQSRnw?e=2h13D2