I was flying through a world I created on the latest snapshot for Minecraft Java Edition when I saw a Spider Jockey with a burning skeleton. It went under a tree and the skeleton stopped burning and when it went back out it started burning again. Then, I noticed none of the other skeletons were burning. I did find them when it was daylight, but I don't think that I found the chunk that they spawned in until it was daylight. Now, in the image with the "(8)" it isn't burning in the daylight. I think I found out why. I did have night vision on, but there is a very large shadow covering the mobs. It is now nighttime and the shadow still isn't gone. I found the two ends of it. (image 11-image12) It isn't a block lighting glitch since I broke a few blocks and nothing changed.  (At least, I don't think it is) It is there even if I set the time to day. I left the world and came back a day later and the shadow is gone and the mobs started burning again.