Full Answer

WordPress runs hooks in priority order — a numbered queue where every plugin registers its code at a specific position. When WooCommerce core or a theme updates, hook priorities can shift. A tracking plugin registered at priority 10 on woocommerce_thankyou might suddenly execute after a payment gateway that now also runs at priority 10, causing the purchase event to fire before order data is fully available — or not at all.

The problem compounds with multiple pixel plugins. Each one — Meta Pixel, Google Ads tag, TikTok pixel — registers its own scripts on the same hooks. After an update, they compete for execution order, and the result is duplicate events inflating conversions or missing events where one plugin blocks another. The shift to block-based checkout in WooCommerce 10.9 made this worse by removing traditional PHP template injection points that older tracking plugins relied on (FunnelKit, 2026).

Server-side tracking sidesteps the entire hook-priority problem. Instead of injecting JavaScript into the front end, a server-side pipeline listens on the woocommerce_payment_complete hook — a stable, order-level action that fires after payment confirmation regardless of what happened on the front end. One hook, one event, fanned out to every destination. That's why [plugin-based tracking architectures](https://seresa.io/blog/woocommerce-tracking/why-plugin-based-woocommerce-tracking-undercounts-30-40-of-conversions) consistently undercount conversions — the fragility is structural, not accidental.