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...