When putting something into your hands and then trying to drop it too quickly, the hand slot freezes up and becomes unresponsive for a brief amount of time.
This is extremely easy to reproduce when swapping weapons, as you can begin dragging the item during the swap animation.
It is much harder, but still relatively easy to reproduce the issue using a random item from your inventory, in this case boxed 5.56 rounds.
I was too slow a few times with 5.56 in the video, but providing you are consistently fast enough the reproducibility should be always.