Guardians not spawning on older ocean monuments

I have a previously generated ocean monument from 1.10, guardians spawned correcly on 1.10, 1.11, 1.12 & 1.13. But now in 1.14 not a single guardian has spawned no matter how long i wait, F3 screen says there are only like 3 entities around, so mob cap is not full... I have optimized the world and even erased the cache but they wont spawn...

Im on normal difficulty BTW. No gamerules changed or anything.

Also general hostile mob spawning is veeeeeeery little...