In a large area I was building, I was unfortunate and came across this bug. A giant chunk of my building was covered in sunlight below the ceiling. It seemed only to affect a single chunk, and I figured that it was one of those bugs where you need to place a light source to fix. Then it got even weirder, because when I destroyed the light source, the sunlight below the ceiling spread across the chunk border. I destroyed the ceiling and built it again, but now the entire inside of my building was covered in sunlight. It got even worse when I discovered that it was server based and mobs started to burn when this happened. I reloaded the chunks and tried other tactics, such as cloning the building and loading the game in a previous version, but it seemed to glitch spread with the building. The glitch remained even without the structure.

How to recreate: Don't know

This glitch looks like something I've never seen before and I couldn't find any way to fix it besides loading up a backup world, but this is a big cost in my eyes to fix a bug.