Amazon returning perfectly good, unsold items as DEFECTIVE

Once again we have started receiving unsold FBA product back from Amazon labeled as defective - with no explanation. Many many individual items. These are bags of pet food, in perfect shape, well within expiration dating. They offer no clarity on why. We are the brand owner. It appears the 3rd party resellers of these items NEVER get hit with the same returns. It is if we are punished for being the manufacturer. Most ridiculous part is that we make Amazon a ton of money. Help tickets are useless. Anyone with insight on how to sort this nonsense out?