The bug

In some cases when generating a chunk, sand blocks generated over lakes being updated do not cause light updates, resulting in large dark spots. Though not mentioned in the ticket, this seems to be caused by the fix of MC-610.

This issue seems to occur most frequently in spawn chunks. A very similar issue also occurs with snow layers over lakes (MC-226437). It is solved by relogging into the world or simply updating the chunk lighting by placing a block, and is completely unrelated to chunk borders.

To reproduce

• Enter the following seed and coordinates (1.17.1):

  Seed: -3202403938531501681
  Coordinates: -174 70 -6
  

  • Alternative: enter the following seed and coordinates (21w37a+):

    Seed: 1938601533716763858
    Coordinates: /execute in minecraft:overworld run tp @s 890.56 65.89 -1014.64 181.20 52.50
    

• Look down.
• → There will be a big dark spot.

Expected results

Sand blocks updating upon world generation should also cause light updates, in order to not create dark spots.