While tinkering with 19w02a, I decided to look around a woodland mansion. The game crashed when I entered a room. When I reloaded it, I found it to have a permanent lighting glitch. Although the room is fully enclosed, there is this one chunk that has zero for block light but 15 (or whatever the time of day is) sky light.

I tried placing and breaking a torch, and I tried breaking and re-placing a ceiling block. Neither made the glitch go away.

Despite being a brand new world, a zip of the world directory is 18 megs, too large to upload here. That could be indicative of other problems. The mansion itself took more than 5 minutes to generate. For the crash, I filed a separate bug report, which is MC-142053.

The world download is here: https://drive.google.com/open?id=1FqWFm6d_nt7lAOp-q97VfU68BEWyEpZt

The coordinates in the room are: -13650 / 65 / -3034