Claudio Dionisi

Xingye Zhang, Two Questions: The world that you found the bug was created in which version? If it was created in previous versions, did you use "Word Optimizer" feature provided in load game screen?

Confirmed for Pre Release 1

I also had the same problem opening a world created in previous snapshot versions. It usually opens the 1st time in Pre 1, but the second time the crash occurs. It seems that the crash is always related to the villager entity in certain chunks created in previous versions of snapshots. If you drop a villager with an egg in the creative mode in these chunks, the crash also occurs instantly. As in the logs posted here, the villager entity is always referred in these errors.

• Entity being ticked -
  Details:
  Entity Type: minecraft: villager (bird)
  Entity ID: 222
  Entity Name: Dorfbewohner
  Entity's Exact location: -756.53, 66.00, -852.33
  Entity's Block location: World: (-757,66, -853), Chunk: (at 11.4,11 in -48, -54; contains blocks -768,0, -864 to -753,255, -849), Region : (-2.2, contains chunks -64, -64 to -33, -33, blocks -1024.0, -1024 to -513.255, -513)

By deleting the villager entity mentioned in the logs with nbtexplorer it is possible to enter the world without the crash, but some chunks are lost.

All errors related to this issue that I simulated in worlds created in snapshots prior to Pre Release 1 have been resolved after using the "Word Optimizer" feature provided in this Release.

When creating a NEW world, I can no longer reproduce the error. It looks like what the bug has solved.
 

Confirmed for 19w14b

To confirm the bug, I tested it on a newly created world on 19w14a.

However, I had the impression that on this snapshot took a little longer to reproduce the bug. I had to restart a few times doing some actions among the restarts, like putting a torch inside the room, removing and replacing blocks from the ceiling, moving around the room, among other things. Only then could I reproduce the error.

But it did not take long, around 5/10 min and 3/4 restarts the error was reproduced as shown in the image I posted.

Confirmed for 19w14a

What I've noticed is that it seems that in certain chunks (always the same for that seed), the light of each block of that chunk always changes to level 15 when restarting the world, no matter how dark a room should be.

The bug is easily reproduced by creating a large empty room that is contained or intercepts the edges of a "light bugged chunk". Even if the room is completely closed and there are no light sources, the blocks contained in the this "light bugged chunk" will have skylight = 15. It seems that between 30 to 40% of all chunks are "light bugged chunk".

To quickly reproduce the error you can use the command below by creating an empty room at the coordinates x = 100, z = 100.

/fill 100 100 100 120 120 120 cobblestone outline

Enter this room without any lighting and restart the world. If the room intercepts any of these "light bugged chunk", upon restarting  all blocks of that chunk will be illuminated with skylight=15 (sometimes it is necessary to restart more than once). Note that this lighting is not just a "visual" bug, it avoids spawning of mobs.

Due to the high incidence of these "light bugged chunk", chances are great to be able to reproduce the error on the first attempt.

PS.: I have not yet encountered inverse situations where the environment is dark no matter how much it is lit by torches or other sources of light. However I have read other issues here about this.

The light system has been rewritten to version 1.14 and this bug is in all the latest snapshots. I believe it will be the last big bug solved before the pre-release version.

Confirmed for 19w03a

Confirmed for 19w12b