Full Answer

The root cause is architectural: WooCommerce exposes lifecycle hooks — woocommerce_thankyou, woocommerce_payment_complete, woocommerce_order_status_completed — and every tracking plugin registers its own callback on 1 or more of them. When 2 plugins both fire a purchase event to Meta on the same hook, Meta's server receives 2 identical conversion signals from the same order. Multiply that across Google Ads, TikTok, and Pinterest pixels, and the inflation compounds fast.

The problem gets worse after plugin updates. WordPress runs hook callbacks in priority order, and a plugin update that shifts its priority number can either duplicate an event (both old and new paths fire) or suppress it entirely (the new priority runs after another plugin already consumed the hook). Neither failure triggers an error — the store owner only discovers it weeks later when ROAS numbers stop making sense.

The fix starts with a pixel audit: open your checkout confirmation page with Meta Pixel Helper and Google Tag Assistant active, place a test order, and count how many purchase events each platform receives. If the count is anything other than 1 per platform per order, you have a duplication or suppression problem. For a step-by-step walkthrough, see How to Audit Your WooCommerce Marketing Pixels.