This happened to me too on my world started in 1.16. Never modified and survival only.
I am also experiencing this issue.
This issue keeps happening on my world (created in Beta, updated through to 1.17, currently 1.18.1). It didn't seem to happen as much in previous versions. "Optimise world" does temporarily resolve the issue but before long the issue appears somewhere else or even in the same places.
Hi, world is too large to attach here, but here is the download link: https://www.mediafire.com/file/odrf86wtjmucoxo/Survive+221.mcworld/file