For products that have attribute combinations, the rich snippets are not suitable for use with Google Merchant Centre/Google Shopping, because only the main product GTIN/SKU/Price etc are rendered and not the variants/attribute combinations, and if Google Ads are running for products, Google is unable to check pricing on the individual variants, and generates errors.
It would be extremely valuable if a future upgrade could render suitable rich snippets for attribute combinations (NB Offer and not AggregateOffer will be needed - see https://technicalseo.com/insights/blog/product-schema-google-merchant-vs-google-search/ (although this refers to JSON structured data)