When trying to store any stackable item such as grass blocks into a container (chests and such) while the chest is receiving the same item from different directions with 4 or more hoppers, the item I am trying to store seems to replace the item that is entering with hoppers causing certain amounts of items to disappear.

Video demonstration <------------

To try to replicate the bug I connected 4 or more hoppers to a chest, all entering the same type of stakeable items and then tried to store the same type of item manually and you will see how sometimes certain amounts of items disappear.