Repro:
Summon a parrot with its Owner tag set to a non-player entity (in this case a villager). The game will immediately crash. The game will crash upon opening the world even after the game restarts.

Example command (replace UUID):

/execute as @n[type=parrot] run data modify entity @s Owner set from entity @n[type=!player,type=!parrot] UUID

/summon parrot ~ ~ ~