EDIT: The problem has been fixed.
It's been brought to my attention that equipping items from the inventory menu (via the equip button) can sometimes cause the currently equipped item in that spot to be lost. This will be fixed in the next update, but I cannot guarantee that will be out soon, so for now do not use that equip button from the inventory menu for a character that already has an item in that slot.
To repeat, the avoid this bug do not use the "equip" button in the inventory menu to equip an item into a slot which already has an item
Thanks as always for playing, and I apologize for the bug!