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This is a tracking implementation inconsistency, not a Google Ads bug.
Some conversions are passing the net price to the conversion tag, others are passing gross. Depends on how your ecommerce platform structures its data layer or what value your conversion tracking script is grabbing.
Check your GA4 or GTM setup. If you’re using dynamic value tracking, the variable pulling the transaction value might be inconsistent across different checkout flows or product types. Sometimes happens when you have multiple payment methods that structure the order object differently on the confirmation page.
Quick fix is to standardize in GTM. Create a custom variable that always strips VAT before sending to Google Ads, or always includes it. Doesn’t matter which as long as it’s consistent. Inconsistent conversion values mess up your ROAS calculations and confuse the bidding algorithm.
Also worth checking if certain products have different VAT rates or exemptions. That could explain why some show with VAT and others don’t if your tracking is set to pass the final checkout value without normalizing for tax structure.
