I have this issue also and it is also repeatable.
Steps to reproduce:
1. create new world, any seed, creative or survival.
2. travel in the world in a straight line, any direction about 4096 chunks. (approx. 2, 1:16 scale maps)
3. watch your CPU usage pin to 100% as you travel.
So as you add more chunks to your game data. the more lag the game experiences.
I had this bug hit me last night. I had 3 picks disappear off my 3rd hotbar slot.
A friend and I were playing at the time. and he was breeding sheep approx. 100 blocks away. And I was sorting out inventory into chests.
The first pick was replaced with 56 wheat. which was funny because I had no wheat in my inventory and neither of the chests I had opened had it either. So I put another pick in that slot and placed the extra wheat into a chest and continued to look for the first pick thinking I mistakenly placed it some where. During this time that 2nd pick disappeared and another stack of wheat appeared! This time it was 54 wheat.
Hmm, Thinking this can't be right, I must have done something stupid, so I placed another pick into the slot and began to to search for the missing picks, opening chests, stoves, and any container I opened since the first disappearance.
And then the 3rd pick I put in the same hotbar slot disappeared with what? A stack of 52 wheat!
So I got suspicious and tried to test this out. was it the pick or the slot it was in. So I went to the zombie spawner that also was about 100 blocks away from my sheep breeding friend and began to kill zombies. This time I put a rotten flesh in that slot and began to accrue zombie drops. during this time the rotten flesh in hotbar slot 3 disappeared and a stack of 50 wheat replaced it. It was then that I asked my friend what he was doing during this time and he said he was breeding sheep and he was down to only 50 wheat.
I wouldn't say this is fixed, but I was able to successfully download worlds from all 3 of my servers yesterday.
I have been unable to download any realms since this morning, 10/31.
I was able to download my world before, as I have been doing since starting a new world.
Each day before playing I download for backup purposes. I have 3 realms going and neither of them are able to complete the download process.
I get the initializing download dialog for a few seconds. Then I get the downloading dialog with 0 MB start and 0 MB end ??, Weird. Also, the progress bar is full but I don't get the play now button. It hangs here at this dialog.
Now I checked the TempData folder and my previous successful downloads are present with the weird looking .mcworld filenames. I do have .mcworld files for the hung downloads, but the are named with a 5 digit number with a size of 1kb.
I just confirmed this on realms.
What I observed is that when you place the new item frame, no sound is played then the crash.
I've downloaded my world locally and confirmed that this does not affect the local win 10 pc version while doing the exact same thing.
After the getting the 0.16.0 update, I have just became a victim of this particular bug. My account (owner) has been disconnecting from server after seeing the 'building terrain' message. I too have another Xbox account that can connect and play the server. but the server crashes if my 2nd accounts player enters a specific area. Luckily, the 2nd accounts player get pushed back out of the area when the crash happens and I'm still able to log back in after.
In this area there is a zombie spawner where we (friends and family) created a exp. farm. The farm is nothing special or elaborate as is contains a redstone delay circuit, a piston, one hopper, and 3 chests. My 1st accounts player was in this area when the server crashed while it was 'farming' exp. there. I believe this initial crash corrupted that particular chunk and now anyone that has to load it crashes the server.
I also cannot download the world as I think this corrupted chunk is crashing the attempt.
Here is a better description to what I've seen.
Find a flat area and dig a one block hole.
Put a hopper into it.
Fill that hopper with cobblestone so it won't accept anything but cobblestone.
Drop a stack of dirt on the top of the hopper.
Place a water block nearby to create a water flow over the hopper.
I should see the dirt get washed downstream, but I don't.
If I do this same thing on the console version. the dirt always gets washed downstream.
The version is 0.15.4
Attached is a screenshot of the hopper with stuff stuck in it