Most Hostile Mobs Stop Spawning

I've seen only about a dozen archers, 10 spiders, and a few creepers and zombies on the surface by day 64. I can run around on the surface all night and not see a single hostile mob. I don't think I've seen as many mobs below ground also. Drowns seem to be spawning as normal. Nether mobs seemed fine also. I've seen about 18-20 illagers. I thought I'd test it by building a spawning room in the sky, put it to hard and wait in the room. Nothing was spawning. Restarted the game and saw 2 zombies, 2 archers, and 2 creepers in the spawner, then nothing again for the last half hour. i did find a cave system i missed. have it lit up. so far no change.