After making a skeleton spawner farm when making the storage system the hoppers I placed started acting odd. When I put items through only exactly half the items made it to the last chest. It's a basic chest storage with 10 chest and 5 hoppers going straight down pointing into each of the chest.
Did some of the items appear in the other chests?
If so, that is normal. A hopper can both "pull" and item from above and "push" an item through its output. The sequence this happens can be somewhat random, so if a hopper decided to push the item before the one below it could pull it, the item would go in one of the upper chests.
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