There appear weird skylight in some enclosure space in old saves

I create a save in 18w47b, and enery time Mojang release a new snopshot, I would open this save in newest snopshot, that is no problem in 18w48a to 19w02a, but when I open it in 19w03a, there appear weird skylight in some enclosure space, even if I break the ceiling and fill it again, the weird skylight is still exist