Hopperhocks will void items when the attempt to merge stacks.
If a stack of an item it is picking up already exists in an inventory, the picked up item will simply disappear, unless the inventory stack is full, then it will make a new stack.
To reproduce:
Place hopperhock next to a chest
Drop a single grass block and wait for it to be picked up
Hopperhocks will void items when the attempt to merge stacks. If a stack of an item it is picking up already exists in an inventory, the picked up item will simply disappear, unless the inventory stack is full, then it will make a new stack.
To reproduce: