When the hostile mob spawning has been patched in the current pre-release. Hostile mobs are too rare to find one (about 10 or less than 20 hostiles are found in one night), especially rare mobs such as Enderman which is extremely hard to find. This issue has been mentioned at 

1. MC-153828

but nobody other than me is not respond to that.

I had this issue on my World that got updated from 1.14.2 version. Haven't tested on a new world