The bug
Like in the images, objects that emit lighting doesn´t emit it. In the first image, if you replace the torches or put a block in the lava will make lights and shadows work well.

How to reproduce it
Create a world in a previous snapshot than 19w08b, but after 1.13.2

Build something, then save the world, close minecraft, and join in your world in 19w08b. It will be shadows in the light that do not have to be there (first image)

Other way to reproduce it is us /fill and fill with air a really big space (second image)