Happened to me today exactly as described in last comment by OcelotOnesie.
I'm on 1.16.0.53 Beta
Running i7-6700, 16GB, 960GTX 2GB on latest Windows 10 build 18362
Sorry, I somehow missed the issue has already been reported at MCPE-64164
My very bad and apologies.
Also to note, I was in the storage room for over an hour, all chunks around my village were loaded for hours
I'm running i7-6700, 16GB, 960GTX 2GB
So Im not suggesting any memory problems or sorts.
Happens to me with slabs as well.
Quartz seems to be affected aswell, but its not that noticeable.
Happened to my friend few days ago in nether, we still not sure how it happened, we had few shulkers on the floor while building and just one of them dissappeared.
Since I wasn't able to reproduce it, and never happened before or again, I wasn't even reporting it. But seeing this issue I don't think he just lost it. Voting and watching, maybe more people will come into the problem and will add something.