Yeah…
Well there are many many known bugs now… Though yes, disappearing cube is a common one.
Sorry for the loss of your item. Blizzard will not take any kind of responsibility for items/characters that were deleted cause of bugs/issues on their end.
Here is a thread that has many many links of people who have lost stuff. Feel free to check it out.
I myself lost too much stuff to even consider playing until it’s fixed. With any luck by ladder S1… they’ll have figured something out… Otherwise… you can just keep playing knowing some stuff will just disappear at random… or even entire characters!!
Stay warm out there travelers.