Could be related to: https://bugs.mojang.com/browse/MCPE-13182

I'm on an older version, and nailed down a more specific repro (I think) so wanted to log here.  Hope it is resolved.

------------------------------------------------------------------------------------------------------------------------------

Steps to repro:

1. Begin game on /gamemode s
2. Fill inventory
3. Change gamemode to /gamemode c
4. Walk over any collectible item on the ground
5. Items on the ground will appear to collect, but will disappear and not be in inventory

Expected result: Items will only collect if there is room in the inventory.  Otherwise, they will remain on the ground.

A few weeks ago, I lost an entire chest this way when I destroyed it to move it, and then encountered the same thing yesterday after going over mob drops on the ground with a full inventory.  I haven't encountered the issue without switching gamemode, so believe this is part of how to reproduce.