The bug
When you use the /fill
command to create a room, or use a structure block to load a structure, the lighting will not properly update inside of the structure.
To reproduce
Go into the sky
/fill ~ ~ ~ ~15 ~15 ~15 minecraft:white_concrete hollow
Enter the concrete cube
→ ❌ Occasionally the room will be partially bright inside. If you open theF3
screen you can see that the client and server light values do not match.
Cannot reproduce in 1.16-rc1 using the command you put in the descripition after trying a dozen times on multiple test worlds.