[MOD]GoldenHelmet might be right on the spot. I can confirm the chunks I have most trouble with are old chunks with 125 entities, more less with other chunks being that range too.
I can confirm:
That are deleting chunks doesn't fix the problem.
Prior chunks to 1.16.1 had problems, but new ones don't.
If you manage to save and quit, the worldfile has it's file size, keep increasing.
The save and quit saving process hangs for minutes unless you just force close.
Though, weirdly enough, in some old chunks, I can open chests, entities moves, break blocks and other actions, and in others, it's the opposite.
Might be related to MCPE-154278
Might be related to MCPE-154278
Might be related to MCPE-142934
It might be related to MCPE-154110 or MCPE-142934
Maybe the new rendering dragon engine is the cause because I can't seem to find any problems with chunks themselves when I checked them using the corrupted world files using the Universal Minecraft Editor, the chunks are normal. The entities might be the problem. Though, it needs more confirmation.
The entities on my world move fine though but I don't.
Experienced the same thing with my MCPE-154729. Build for a few hours outside the future corrupted chunks, have a nether portal with a bunch of entities like chests near it and you got your recipe. I guess having many builds near it will also factor in.
The new update 1.18.31 works. Mine was a bit laggy at first due to how many entities I had per chunk but it worked. It slowly stabilized
It is all fixed and also the save file decreased from 390+ MB to 379 MB.
The devs really fixed it fast.
Edit: I also tried multiple world copies of my previous attempts at trying to fix the chunks (10 copies) and it all worked fine