How to reproduce
1. Spawn a wolf
2. /execute as @n[type=wolf] run data modify entity @s Owner set from entity @s UUID
The game instantly crashes and does so again every time the world is subsequently loaded.
This happens with cats too.
I want my pets to experience this: 🙂
[media]
This also happens with 2 entities owning eachother - I tried to set the owner of a tamed wolf to the wolf it owned, and it caused an immediate crash. Log attached