On the realm I play on while I was building a roof all my game GUI disappeared, including d-pad, hotbar, chat and menus. Also all entities disappeared, I only saw the circular shadows underneath them. I was only able to see blocks and (no idea why) the item I had in my hand. After relaunching Minecraft it was fine for a few seconds, but after I started walking it happened again. I broke a few fences, then relogged, it was OK, I was able to chat, but I better didn't move. I asked other people that were online for help and they destroyed most of the fences, trapdoors and fence gates that I used in my builds. Then it was fine. I think it's caused by fences (I had over 4 stacks of them used in my builds), maybe also by fence gates or trap doors, possibly stained glass. But I think it's fences. It only happened to me, the person that helped me breaking fences didn't have any problems with GUI disappearing.
The same thing happened to me on a different realm back in 1.0 version, also in an area where we had tons of fences.

Device: ASUS ZenPad 8 (android 5.0.2)
Minecraft gamertag: DeenyBuilder
Version: Better Together 1.2.3, it happened on a realm