When you throw an item into a hopper/hopper minecart that is used to filter items, it only tests if the first item fits into the hopper ignoring all other items that are thrown on it. For example, if you have a hopper that is sorting oak wood, and you throw a piece of ice on the hopper, the hopper will be focussed on the ice and will not take a piece of oak wood until the ice is removed. This has messed up my piglin bartering farm and has probably affected many other players who are building restone storages.