I also had this problem. But, as a matter of fact, the chest was not invisible and had loot in it.
This is fixed in the iOS version of 0.12.1 .
I think I the report is thing about "Block Launcher". Please note that block launcher has nothing to do with Mojang (Directly).
I do not get what the report means, too short to be read.
What does this report mean? Confuses me. Soul sand pistons? Redstone & more? What bug is this?
Maybe it is a block lag? I do not have a screenshot because the spawner entity despawned.
I found another way to fix it.
I put a glowstone block on it and after 2 minecraft days, it disappeared.
This also affects v0.11.1
(Maybe)
This issue also duplicates:
1) MCPE-10971
2) MCPE-10792
3) [MCPE-9937]
4) [MCPE-9822]