Lg Nexus 5x
If this has already been mentioned, I apologize. I searched and couldn't find a report for a bug like this.

When moving items to or from my inventory to or from a furnace or chest, other items in my inventory will disappear, usually the item in my first hotbar slot and my tools. The item in the first hotbar slot will also randomly disappear during gameplay. As far as moving items go, it seems to happen if I'm holding down my finger to transfer a whole stack at once, but I don't know if that's the only time it happens.