I have searched the issue tracker and not found my exact issue, but please forgive me if it is there and I simply didn't see it. I would honestly be surprised if it wasn't as I've experienced this bug for many, many versions.

While exploring Minecraft worlds, I occasionally come across single chunks, or on one occasion two side-by-side chunks, wherein sky lighting does not seem to work. The light radiates in from the sky-exposed blocks at the edge of the afflicted chunk(s), but no blocks within the chunk receive sky light - it's as if they're in the shadow of an object over them, but I have dropped myself from above the build limit all the way to the ground on these chunks and encountered no blocks at all.

Placing light sources such as torches works exactly as expected, casting light both within and out of the chunk boundaries, There appear to be no problems with generation or spawning within these chunks that I have noticed. No mobs spawn in them because they're not a large enough space for the light level to hit 0, the lowest it reaches is 7 due to light from the skylit blocks at the edges. Upon removal of whatever light source was placed, the chunk resumes darkness.

If I teleport far away so as to unload the chunk(s) and return, the issue is fixed upon the chunks being reloaded. It's not a serious issue by any means, but as a programmer myself I know that it's no fun to have a bug in your work, so I figured I should go ahead and report it since I didn't find it on the tracker.

Edit: The location in 3 of the screenshots is seed 4673280703031584019 Large Biomes, X=132793 Y=88 Z=131223. I don't know if it will happen in the same place or not but I figure it's worth dropping the location here.