The chucks never generate or don't load. This issue seems to affect multiple areas. My seed was 4976586551792305041 btw.
Some screenshots are attached.
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It seems like they are generating (failing to load in the client) because I can view them in mcaselector without a problem, but can't use the world.
Saving the world did temporarily fix the problem. It was likely a server crash like I frequently experience in 1.16.5

Yep, seems to be the same