In the video I have attached to this, you can see that the torch light doesn't update until the chunk is reloaded. I'm at Y-level 243 by the way.

Minecraft Version: 1.20.4
Shader Version: 8.8e (Still applies for 8.9a, the video was recorded with 8.8e.)

Updating lighting is not the responsibility of the shader. The shader only takes the value reported by Minecraft. The problem must be caused by another mod. You will see the problem in any shader that does not use its own global illumination.