They changed the way they handle drops and items as JustAnoobROTMG said.
If you try to pick up an item too fast, it won't count as you picking it up. I always drag the items into my inventory to make sure
What to do to make sure you have it-
1. Go away from people (make sure no one is around) and drop the item... If you actually have it, it should have dropped.
2. If you drop it and nothing happens, simply just go back to the bag and pick it up again (I suggest dragging it into the inventory)
Without equivalence, nothing is possible.
*I am not MrMagma, I found this guy in Realm of the Mad God and asked if I could use it as a username*