This has happened to me three times. Hostile mobs are not spwaning at night and I've made sure that the difficulty isn't peaceful or anything like that. It's very random, sometimes they spawn sometimes they don't. I've also tried to move somewhere else.
Environment
Windows 10, 19w13a
Linked issues
duplicates 1
Comments 2
Duplicate of MC-139338
Set your Render Distance to 12 or higher, that should fix it.