I have created a creeper farm that is between y 108 and y 123. The on the ground level (y70) the shadow under the farm is correct. I have create an AFK spot that is way above the farm (y194).
The problem is that the shadow my AFK platform casts is offset about 16 blocks to the north when the world is loaded. If i climb all the way up to my AFK spot, and then back down, the lighting is correct again...until i next load the world.
The first screen shots shows the shadow on the ground (just dark enough to spawn mobs) and the second screen shots shows me standing in the middle of the shadow looking straight up (notice the Sky light level on the debug text is 7).
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I noticed in the last couple of snapshots, but I figured it was known issues with snapshots. I couldn't find any other bugs like this so i opened this one.
After backing up and optimizing the world (i ticked the Erase Cached data too), the problem appears to have resolved. I will comment here if it reappears in the future.

There were a few issues in previous snapshots with lighting, so it might make sense that this fixes it - I will also reopen it if we receive any further lighting issue reports like this.
I experienced something similar to this in 1.16.3: I have an enclosed bubble column that goes up to build height and there are spots to the South and sometimes East that have low sky light despite nothing being above them. Going up to build height does not change the light levels at ground level (y=62).
The issue goes away if I use Optimize World (and erase cached data), however, I can bring it back fairly easily by going into the Nether (unloading the area) during sunset. Returning from the Nether during full daytime doesn't seem to change sky light levels at all; I didn't check returning from the Nether during full night. I can probably put a copy of my world save on my google drive and link it if that is requested.
In the screenshots I attached, I had two areas with these lighting glitches before optimizing the world. The glitches appeared after a fall damage death (near one of the water columns) unloaded the area. The torches were placed in areas where the sky light level is 7.
Area 1 before optimize world is the area to the East (two blocks at sky light level 7).
Area 2 before optimize world is the area to the South (several blocks at sky light level 7).
Area 2 after optimize world is just showing the sky light level being restored to 15 (this happened for area 1 also).
Waiting for Chunk is just noting that immediately after Optimize World or returning from the Nether, the light levels are replaced with that text until you move around.
Area 2 after going to Nether is a new (larger) area of low sky light (in about the same location as Area 2) after returning from the Nether during sunset. Area 1 stayed at sky light level 15 this time.
Never mind on the comments mentioning sunset in the previous message. I reran optimize world and then went into/out of the Nether again during early afternoon and got another lighting glitch (slightly larger than the first one and much smaller than the second one) in Area 2 from the previous message.
If the issue is still occuring in the latest version, can either @unknown or @unknown please attach the affected world?
I must have missed the original request last year to check if the issue is still occurring.
It is indeed no longer occurring in the world I took my screenshots from. However, I have not expanded the building there to reach the new build height limit (the top is still at y 255). I do have other structures that reach the modern build limit, but the blocks at the top of them are transparent - I haven't seen any lighting issues around them either.
Check if using "Optimise World" fixes the issue permanently. Also, has this been an issue in previous releases?