Replace spawned cow with ravager with noai

Hi, I've tried lots of combinations to do this based around creating a custom cow mob, then OnInitialEntitySpawn event, despawning it and using the command:

/summon minecraft:ravager ~ ~ ~ {NoAI:1}

This works in game when manually entering the command, but when put on an event, it crashes the whole game and quits.

I've also tried "despawn entity", then "Spawn at X Y Z Entity: Ravager"  but that crashes too.

Thanks for any help.