Hi,
Thanks for reporting this. A loader in the base game uses the same collision mask as a belt (it calls collision-mask-util::belts()) which is 'floor, meltable, object, transport_belt, water_tile'. The miniloader uses only 'transport_belt' because it must do so to connect to the belt (you get an error otherwise).
The Advanced Furnaces mod uses 'item, meltable, object, player, water_tile, is_object, is_lower_object' which does not seem correct (there should be a "transport-belt" in there) and that has no overlap with the miniloader so you get this error.
This should be fixed by the Advanced Furnaces author (They need to add "transport-layer" to the prototype or (better) call collision-mask-util::get_mask('loader-1x1') to get the correct collision mask for their loader.
