MemoGoodNameYes

This happened to me (as the host) after changing the world to Friends of Friends from invite only - it's a creative world and I have a play timer on a scoreboard so I could see I had been added as a totally new player (now showing as "Player Offline").

Upon restarting the world I was back to normal, but the "Player Offline" that was created is still there.

Edit: I joined someone else's multiplayer world to try and troubleshoot multiplayer issues I was having, and when rejoining my creative world I was back as the totally new player (the same one). Leaving and rejoining put me back to normal again.

Edit 2: Every time I join someone else's world the first time I join any world I'm there as If I'm a new player. This may help with recreating the bug

1. No tools used on any.
2. World has not been on a realm.
3. This has happened on 15+ worlds for me - all (as far as I remember) last loaded 2017 or earlier.
4. No. Don't believe ticking areas were around that early.

Possibly related to MCPE-85039, MCPE-87376, and MCPE-87503 which are related to chunks that haven't been loaded in a long time.

Harming potions don't give a status effect - they just do damage. So if a witch threw a harming potion no effect would appear.

The biggest issue I personally see with it is that it could easily be used by players with creative mode access to grief things quickly, and to create explosions when these have otherwise been intentionally turned off. If this isn't a bug, maybe a gamerule could be added?

I still think this is likely a bug however.

It feels similar for me. I think the input delay might have increased. No way to measure it though so I'm not sure if it has increased or not

on the side note said by madegeeky, this issue was seen in the beta versions as early as september, but not in the actual game until a release in the last few days.

I tried changing from the Nvidia GPU to the Intel one, but for me that didn't solve the problem. Frame rate was noticably worse (but that was expected), however there was still bad input lag.

Alfred Osborne's comment fixed it completely for me (nvid 1060). Obviously not ideal playing w/o smooth lighting etc but it's playable now.

I also did notice (before fixing it) that the mouse input lag also exists when the mouse is in its normal mode (e.g on the worlds menu/ in the settings).

This is definitely something to do with rendering. I updated all my drivers. I have Intel UHD Graphics 630 and NVIDIA GeForce GTX 1060 and 16gb ram.
Been playing on console instead, which doesn't seem to have this problem. Hopefully this is fixed soon.

I uploaded a file that shows where the invisible chunks are. Everything past the red line can be entered, and there's water particles there, but it doesn't appear visible.

I attached a .zip file containing the world. Some parts of the world are full entirely of invisible blocks, and the world crashes. It isn't the exact world I used earlier, but exhibits the same behavior.

I've checked some of my old worlds and haven't seen this issue personally in 1.16.40, what version are you on?

The fix won't put back chunks that have already been deleted.

Edit: I think there is still some issue here, very old worlds (unopened since July '14) are still taking a long time to open and save, but the issue is definitely more minor than before.

Worked fine on 2016 world. Unfortunately on worlds with existing chunk errors there is no easy fix, unless you go to a backup.

However, loading a world from June 2014, it is taking forever to load (20 mins so far). After about another 5 mins i force closed Minecraft and started it back up. The world loaded after 5 minutes on the second try, with no corruption issues. So I believe the problem is mostly solved, but it still took a very long time to load that.

Hope this helps the devs, I've been able to answer a few of these questions.

It appears it happens to all chunks that have not been loaded since ~2018. This bug did not exist (to my knowledge) at all in 1.14.60.

The problem is much much worse for worlds that are pre-0.9.0. The world takes around 10 minutes or more to load before loading a world with no chunks whatsoever. Trying to make the world infinite crashes the game immediately, and the game only manages to rename the broken world to [world name]-old, created a new folder called [world name], then crashed.

The corruptons can happen to worlds of any size from what I've seen. I've seen it happen on Old style worlds, superflat, and infinite worlds ranging in size from barely over 0MB to more than 200 MB.

The best solution to the problem I have seen for players is to, using a backup of your world (or a copy) from before the corruption, either by:

A) Use an external program (such as MCC Tool Chest) to convert the world to Java Edition, then convert it back to bedrock. This will erase anything in chests, may glitch doors, glass panes, and will remove any exclusive blocks to bedrock, like old stonecutters and nether reactor cores, but at least you'll have the world. Keep the original version for when they fix the bug.

B) Open the world on a device with an older version (1.11 worked for me) and load in all the chunks on your world that you don't want to be corrupt. Then it should be safe to open on the modern version. Make a backup though just in case. You would need to have an old device that's been offline for a while though.

Unfortunately, if you're on console, I'm not aware of any way to do this. If you do have a copy of the world, DO NOT LOAD IT. As long as you keep the world unloaded, it should preserve the files, and the world will work when this is fixed.

As for 1.16 local worlds being affected by this issue, I don't know. I haven't seen any, but I'm not sure that none exist. I haven't personally made many worlds since then, most of my worlds are much older.

Quick edit/update. It does not only happen in older worlds. It can happen in more recent worlds also. It just isn't guaranteed.

Similar bugs are occurring with older worlds that have not been loaded since pre-2018. Those are being tracked at MCPE-87503 and MCPE-85039.

Temporary fix (but mojang should still fix this)

Load the world in MCC Tool Chest PE.
Convert the world to Java edition,
Load the world in java (although you may not need to do this)
Convert back to bedrock

Save as a new world file

Should fix the corruption issue

This would have pretty major ramifications for griefing though, wouldn't it?

If I had to guess, I'd say it has something to do with the air being in either corner. The villager might think they're already indoors.

Unable to verify
Uploaded renaming.png