Hi guys,
I've found a bug in the campaign.
When you finish a campaign map that gives an Item and your inventory is full, you select the option to drop an Item, when you do that, the menu in which you select the item to drop appears behind the previous menu therefore you can't drop any item because you cannot interact with that window.. so you lose the item from the mission.
I use the resolution of my laptop 1366x768 haven't tried any other resolution to see if it makes a difference. This happened on 2 different heroes.
Until this get's fixed please make sure you always leave an open slot in your inventory.