Joby Walker

I'm seeing the same thing, though the world worked just fine while working on a witch farm away from spawn but after coming out of the Nether near spawn the exception occurs. World: https://drive.google.com/file/d/1v0-ili6QtRV3USdUgF6jGBSu7kPbMLzN/view?usp=sharing

Like the same as: MC-125900, MC-129682, MC-129792

Sorry about that too many windows... This relates to: MC-125900 and MC-129682

World file: https://drive.google.com/file/d/1-36lVztVp6yjFtyOjuxXWrqC8L0S6K-F/view?usp=sharing

18w16a world upgraded to 18w20a then 18w20b (still seeing this under 18w20c), There is a skeleton spawner at (-19 55 129), with the killing floor underneath. Even though there is no light in the spawner chamber it is well lit.

This seems to happen because all areas are getting skylight access and that never changing.  This means underground slimes will spawn like crazy, while other mobs just don't happen. Attached image showing an underground area with skylight level of 14.

This is the same as MC-129792

I'm seeing this too. I believe my version was created in 18w16a (maybe earlier) but was run under 18w16a for a while and then this 18w20a/b/c cycle.

Attached a snapshot showing in an entirely enclosed area with no sky access the light is set to 14 (from 14 sky access) even though the only lighting should be the 9 block light.

This is killing spawning except for underground slimes.  I AFKd over night at a mob farm and got zero drops.  Thing worked just fine until 18w20a (though didn't try the 18w19 cycle because of the loading issues from 18w16a)

I'm seeing the same thing in an upgraded 18w16a world where spawning is extremely rare and spawners don't seem to work.  The only exception is a partially built Slime Farm that is producing huge amounts of slime balls.