When generating multiple structures on large scale the block lighting is not correct.
Somtimes it just has a border where it goes completely dark and those are not the chunk borders. This also happens in chunks that are loaded by a player.
I could encounter the problem in all Pre-releases and in 20w22a. Before I found there to be no problem at all. Singleplayer as well as Servers are affected
On rejoin the lighting is fine again