When the darkness effect disappears, before you can completely see the sky, there is a "mist" existing for a split of a second and after it disappears you can see the sky.

Steps to reproduce:
1. Make yourself above the ground level or go into a big cave (big enough so that your render distance makes you see sky after the distance.
2. Either stand on shrieker (can_summon:true) or type command /effect give @p minecraft:darkness 5 1 true
3. After the darkness effect ends, the line of sight moves forward, then out of a sudden stops, making you see the "mist", and only after it disappears, you can see the sky.

I got no resourcepacks turned on.