When you take “Cube monster Parts” “Mechanical Parts” “Animal Bones” “Stink Sac” or the “keys” they don’t appear in your inventory.
This makes the player unable to drop these types of items. Being very problematic for maps like Bed Wars.
@WeilonYT Thank you for your report! We would like to look into this further, would you be able to submit a bug report using the form available here? Fortnite Creative
No problem. I also sent a report there yesterday 
I’m having this same issue.