I think looting needs to prioritize loot over ammo when quick looting. Even better I think it should work as follows:
1) Crate
2) Complete full stacks of similar items that you currently have in your inventory.
3) Loot based on rarity
4) Fill the rest of empty slots with whatever ammo is left...(as well as weapons)
Some times it takes waaaay to long to loot death crates, and if you select all I think it grabs from top down and leaves all the resources behind.