Still after a few updates we’re getting an empty loot once or twice in a 10 times session.
However, I’ve also noticed that if I haven’t unlocked 
(if I can use this term) an item, I won’t get it during my loot sessions at all doesn’t matter how many times I loot.
@marspark is there connection between these two?
Thank you for your feedback. When you say unlocked, do you mean you don’t have the item in the bag?
more I haven’t had at all in my bad. If I haven’t received it after winning a battle.
So if I don’t have before the loot in my bag because I assigned it to a hero or deleted it, I still have a chance to get it during a loot session.
If I’ve never had an item in the bag, I don’t get it during my loots.
You mean you aren’t getting new items that you don’t currently have? You’re only getting duplicates from loot?
Yes, only duplicates from the loot. Also, I get a lot of simple items mostly rings looting stage 10. I might get a new item only after a progressing through the story. I’m currently going through nightmare mode btw.
I think certain stages are more likely to drop certain things, try different stages to see if you get different things.