I did notice the flickering while testing, thanks for adding the video.
I can also check at which angles the fog appears and disappears at if you need
I believe this is because of another bug which does not recognize older structures. 20w21a changed the names of all structures to remove upper-case letters, which means the game doesn't recognize structures with upper-case letters.
Wither Skeletons can only spawn on nether bricks. The netherrack is what is preventing them from spawning. I hope this fixes the problem.
Currently, baby hoglins deal the same damage as adult hoglins, similar to the zoglins.
It appears that the fog unrenders above 0.33 and at/below 0.38 at 1 block intervals. For the sake of the next explanation, I'll call these areas "pockets". The area in which you can look while the fog is unrendered expands the higher up in the pocket you are. Towards the bottom, the area is restricted to only -90 in the vertical orientation axis. Towards the top, the area expands to just above -55 on the vertical orientation axis. This may be somewhat irrelevant but still adding it in case it aids in fixing the issue.