We have a snapshot server running 14w11b and yesterday we noticed a severe lack of hostile mobs. walking around at night i only see 3 or 4 mobs at a time. when they are killed another 3 or 4 spawn. we have a natural mob spawner above y185 and 1 or 2 mobs are spawning very irregularly. sometimes up to a 15 minute wait for them to spawn. we have changed the server to peaceful and back to hard again to possibly clear out any "stuck" mob problems but it hasnt helped. everything was running as normal up until yesterday.
Linked issues
duplicates
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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

Ok, thanks for the feedback.
Is this occurring with multiple users logged into the server? If possible test with a single player and see if the issue persists.