"Not enough buyers..." and "not enough raw materials" close to each ...
Try even more silos. If set to empty and the silos are still at 100% the silo's trucks are 100% utilized exporting goods to empty the silo. Try dropping down a lot of silos in the area such that each one only has 1 or 2 trucks in circulation at a time. There may be an initial inrush of trucks to deliver/fill the silos, but once balanced ...