One way to check for material issues is to switch to a different lot of material or even switch to another color material. If the issue is isolated to specific lots then it is critical to contact the material supplier to help with the investigation. Another important thing to keep in mind is that if the issue is in the raw material or color concentrate you will probably experience problems on any job that is running the material. Keep in mind that there are cases where certain molds will show a defect much faster and to a greater severity than others, so what may create 10% scrap on one mold may only cause 1% on another.