This issue just seems to be at one location at my old outpost. And was only an issue since the hopper's were tweaked. Before that, not a single issue. Ever. At my current outpost, I have not had a single issue with this same build. Good call. When I get a moment I will alter my gold farm's sorter to the one you use. I think the issue is simply just the single hopper used as the sorter. Baffled as to why it would start to fill when the below hoppers are empty.
Little Helpful Tip. Rename a stack (or bunch) of snowballs. I always call mine 'spacer'. This will help you see if any of the sorters fail. Also it will let you sort snowballs if you want to. For items that stack into 64 - Place 3 spacers in Slot 2 , 3 & 4 of your sorter. Place 2 spacers in Slot 5. So 11 spacers total. Then you need only 1 of the item you are sorting. For 16 stack items - you need to do 3 spacers in slots 2 & 3. Then 2 spacers in slots 4 & 5. So 10 spacers total. Again 1 item to actually set the filter. In either case - you sacrifice 1 item to the redstone torch, but now you are using 2 instead of up to 42.
Fantastic idea! Going to replace my "sorting sticks" soon! Never thought to use an item that has a lower stack limit to have less of the item that I want to keep in the hopper. Mine shall be "sorting snow"
