Underground shading issue, added SS of my settings in the gif. If you need a static picture of it just reply, but i'm lazy.

https://gyazo.com/111209b55bd9361d324c387824e2c737

(EDIT)

It'd appear that this bug is fixed when replacing the torch/adjusting the lighting. It won't work if i just break the blocks, but replacing a torch seems to fix it. I think the way this could be caused may be with regenerating the terrain in the area? I'm not sure. Also, I'm pretty sure this is an old bug. Feels all to nostalgic.