Fishes, Loot Treasures and Hostile Mobs don't spawn

Fishes don't spawn at all, although there are turtles and dolphins.

A treasure map leads to a point but the treasure chest is missing.

Hostile mobs normally spawn in caves but on the surface, during the night, they generate a maximum of 2/3 in a very large area, or sometimes they don't spawn at all.

From 19w12b instead everything works properly.