Affects Version/s: Minecraft 19w02a
Fix Version/s: None
Hostile mobs fail to appear, but can deal damage to the player. Potentially immune to damage (couldn't see it, didn't hear it take damage-- may have not been hitting it)
No problems with passives (yet)
Similar bug reported on Xbox One, where any mobs (and items) hostile or passive would dissapear close to the player.
The key difference is they never appear in the first place, it spawns invisible from what i've noticed.