When you have a full inventory (100/100 for instance) and get items forced on you through quest rewards or story moments, you will actually go over 100 (102/100 for instance) You will get those items in your inventory. You just won't be able to pick up/loot or buy any items until you've moved some items out of your inventory (sold 3 items to get back to 99/100)
So if you haven't gotten an item which you think you should've gotten, that may be a bug and you should contact support.
