I loaded up a backup of a world which was first generated in 21w05b so I could look around random chunks I had explored but not done anything in because I planned on resetting some old chunks for when the 1.18 snapshots come out. (I haven't actually edited the save files in anyway yet.) The particular area in which this occurred was loaded once in 21w05b and was not loaded again until now in 1.17. It is about 1 km from my base but I rarely ever explore, especially in that direction because there is nothing really interesting in that direction. However, when I went in spectator mode and started exploring, I found a single chunk which has no skylight from it. 

This reminded me of the bug MC-214793, but this was different in that it had skylight protruding in from the adjacent chunks and it was only one chunk. Also that bug was fixed in 21w18a and the one I experienced occurred in 1.17. Reloading the world fixed the problem, so I am 95% sure it was caused by loading the chunk in that instance, not from when it was generated or loaded in the past. I have seen this bug occur two other times in this world but it was during the era of MC-214793, so I assumed that was the cause. However, I have never seen MC-214793 occur in this particular world. Also, those two instances were within about 100 blocks of my base.

I forced a crash report which will be attached. Screenshots will also be attached. I have included one of the sky to show that there is nothing above that may be blocking the light in anyway.