Step to do the bug:

1: Creative mod only

2: Open the inventory

3: Drop some item (only work by pressing Q)

Now when dropping, you will see that sometime an item drop (not everytime)

4: Pickup the items and see that you miss some (I tried 3 time and you pickup around 18 items (change depending of the speed of dropping)

ONLY WORK if it's in creative mod, if the inventory is open and that you press Q to drop items (Should work with Ctrl+Q)

I only tested on 1.14.4