this happens with single player or multiple players. i first noticed it when i was on by myself and the natural mob grinder spawned 4 mobs and stopped. later went down to the ground and walked around at night and mobs were scarce. btw when the grinder was first built it would have 75-77 entities in the collection point. last week i noticed it would only have around 60 when they stopped spawning. all these are single player numbers. thanks for the quick response. i dont know if it helps but local difficullty is showing 2.25 (day666)
this was the bug listed in https://bugs.mojang.com/browse/MC-2536
server view distance was changed to 8 at one point in time. changed it back to 10 and problem disappeared
Resolved