Magento - Products not sticking to the categories -


we partnering external vendor implement ecommerce site in partnership our supplier.

we have 2 inhouse ecommerce stores linked same admin. in new store, products not seem stick categories @ all.

every go test new site , notice on 90% of products have lost category mapping.

any ideas going on here?

additional info - master repository of data our erp system. product information flows magento via middleware. have verified time , again through our testing category mapping not being touched product updates via middleware.