Same issue in my world. Skylight patches sometimes can be seen by creating a large hollow cuboid with command, such as "/fill ~-20 ~-1 ~-20 ~20 ~10 ~20 stone hollow". Issue appears both in newly generated worlds and those updated from 1.13.2. Hope this will help.
cfy
Same issue in my world. Skylight patches sometimes can be seen by creating a large hollow cuboid with command, such as "/fill ~-20 ~-1 ~-20 ~20 ~10 ~20 stone hollow". Issue appears both in newly generated worlds and those updated from 1.13.2. Hope this will help.