Mobs spawning inside the Ocean monument

Hello Mojang Studios! Recently I upgrade my Minecraft world to the 20w21a snapshot and when I went inside my guardian farm storage (I drained the whole monument and did a storage there) suddenly a lot of mobs (creepers, skeletons, zombies and spiders) started spawning as usual, I tried to create a new world in the latest snapshot and see if the same happened, it did not, but I just tried with a small section of the monument, I don't know whether that´s because of the mob cap or not, but anyway it was a very uncomfortable situation