Hostile mobs spawning in areas that should be "secure"

Since 1.16 was released, hostile mobs are spawning in well lit rooms. Seeing Creepers, Spiders, Skeletons, etc all spawning (and at an alarmingly high rate) in rooms that have always been "secure" in the past.

In one example, I left a smallish (maybe 30x40 room), previously secure area for a few minutes and when I returned, there were no less than 2 creepers, 3 skeletons, 2 spiders and a witch all attacking me! We literally were not able to repair the damage as fast as the creepers were inflicting it... and this was EASY mode! Have had to set to Peaceful as it is now completely unplayable otherwise!

 

Details: XBox One console

World: Created in 1.14

Multiplayer: Yes

Mode: Survival

Difficulty: Easy