Hello,
Because the “fit doors” and “fit windows” are two slots that consume a lot of various items, they are extremely difficult to satisfy logisticaly. It proves even more difficult when the load balancing on the resource imports is bad (the resource importers aren’t used with the same kind of load, and that also goes for importers adjacent to one another. (I’m not you, but I might have based the choice of the importer based on the time it takes before the slot can get the needed item instead of the proximity to the importer)
Moreover, it doesn’t seem like they can make proper use of stockpiles that I’ve added to accelerate the dispense of these slots (orange vs magenta arrows). I believe that an order put at an importer should be cancelled if a nearby stockpile just replenished.
Ps : you should add a “configure import” options for the stockpiles too. It annoys me that they won’t import from the factories which are on the other side of the map and dispense it localy.
My compliments on your game. 
