Version Info:

• Minecraft 1.16
• Item Collectors 1.0.9

Description of the Bug:
Placing a chest, hopper and a item collector as the picture below and break a block on top of the hopper will dupe the item. Probably due to item collector collects item at the same tick as the hopper = two items.

Steps to Reproduce:
See picture below.

Screenshots:

Tested some more, dupes by dropping a item as well. See below setup:

Apparently hoppers only set item entities to dead and don't remove the items from the item entities. I was only checking if the item entities still had items. I changed it so I ignore dead item entities.
It is fixed now in version 1.0.10.

Thanks for reporting the issue!