Inside a region file, each chunk has an "InhabitedTime" value which is supposed to increment each tick a player stands in a chunk.
I've created a 21w40a world and explored it a bunch in creative and spectator mode. Upon examinating the region files using NBTExplorer, I've been able to constate that none of all the stored chunks Level.InhabitedTime values have incremented, they are all still at 0, breaking Local Difficulty.
Comments 3
Those two issues are unrelated:
MC-127407: Affects "Some chunks", while this issue affects the entire world, no matter how many chunks or region files are generated the value stays at 0 everywhere.
MC-197433: This is a report that servers don't update the client on the local difficulty for display on the debug menu.
Duplicate of MC-127407 and MC-197433.