I have an area where boats are lined up close together in a row with one trained horse in each of them, each horse is on a lead tied up. If you go to the nether then back to the overworld the horses are either out of the boats walking around, or some boats have two horses in them. I go to this area in a copy world to test as i don't want to go in my world and undo hours of work setting everything up again.

I have re-created this issue as it was closed as duplicated, but the linked report was not the same issue as mine, also it was on realms on windows, after extensive testing, i have no issues with villages, pillagers, zombie villagers ect leaving boats when re-rendered in the world, the only issue i can see is Horses although i haven't tested every mob, just the regular ones.