MOB SPAWNING

What I expected to happen was...:
Mob spawn like 1.13 version

What actually happened was...:
mob don't spawn or spawn rarely in chunk , only after i save and go back to menu and reload the world mob spawn in that chink, but later mob don't spawn anymore yet... i play in difficult mode and no mobs spawn... neither pillager... and villager have problem to breed... 

Steps to Reproduce:
load a world wait for the night and walk around the cunk... mob don't spawn in other chunk after your then killed them mob don't spawn anymore