As per the privacy sandbox guidance, buyerAndSellerReportingId will overwrite buyerReportingId when generateBid does not return selectedBuyerAndSellerReportingId.

This is unexpected because buyerReportingId contains information that buyer does not want to share with seller. If an ad contains buyerReportingId, buyerAndSellerReportingId and selectableBuyerAndSellerReportingIds but generateBid does not return selectedBuyerAndSellerReportingId, buyer still wants to know buyerReportingId.