Bug Description

When placing and removing light sources near the positive edge of a mostly empty chunk, that chunk will sometimes not be lit correctly until it's mesh is otherwise updated.
Update: this seems to also apply to some of the neighboring blocks as well, the rules as to what it applies to aren't fully clear.

This issue presents both with and without Iris and LambDynamicLights, and is especially egregious with LambDynamicLights. I've seen and confirmed this issue on 1.21.1 and 1.21.11 so far, and I did confirm all mods installed are fully up-to-date (Sodium 0.6.13, Iris 1.8.8, LambDynamicLights 4.8.7).
Update: this issue appears with no other mods installed, including Fabric API. It also applies in Minecraft 1.21.11.

Reproduction Steps

Use Sodium 0.6.13+mc1.21.1 or 0.8.2+mc1.21.11 on fabric

Generate an empty world (or generate the void flat preset and remove all surrounding blocks).
Place a block at -1 0 -1 (or any position relative on a grid of 16 blocks), and place a block horizontally adjacent to it inside of any neighboring chunk.

Place a torch on this block and remove it until the incorrect lighting appears.
Alternatively, install LambDynamicLights and move around near the block while holding a bright item, and it will flicker and sometimes be left in the wrong state when you move away or remove your light source item.

Log File

latest.log

Second log file with no additional mods installed:
latest.log

Additional log file in Minecraft 1.21.11:
latest.log

Crash Report

crash-2025-12-30_06.43.58-client.txt

Second crash report with no additional mods installed:
crash-2025-12-30_13.54.18-client.txt

Additional crash report in Minecraft 1.21.11:
crash-2025-12-30_14.03.10-client.txt