I went to an ocean monument to try to dry it and I noticed no guardians were spawning. At first I thought it was because I was nearby, however after I got on land and waited for the night, the common agressive mobs as zombies, skeletons, creepers, spiders and so were not spawning. Phantoms were not affected.
I could not find any report of this early version about this issue.
Related issues
Comments

This issue is crucial, finding monsters in overworld feels like I'm playing in easy-peaceful difficulty (I'm on hard mode)