When having multiple mobs on a looping minecart track, then getting multiple blocks away, they gather into a single block space while still looping around. Here is a clip of the issue: https://1drv.ms/v/s!Aq2tw4NnTnf6lViXeirgkjXafzbb?e=vjfmcY

How to recreate the issue:

1. Put at least 6 mobs in minecarts onto a single looping minecart track
2. Fly or run a 20-30 blocks away and wait
3. Repeat step 2 around 3-5 times