I would start by contacting the vendor and explaining the situation. They will normally have an explanation on what’s going on with that particular lot of packaging. Being that they are the primary vendor, I’m assuming that their process capability was tested. This would give you an expected DPMO and confidence in the vendor in the first place. Continue monitoring the packing as they arrive, and if the situation occurs again look at alternate vendors (who may or may not have been vetted when the initial selection was completed).