Full Answer

When ROAS falls off a cliff overnight, the instinct is to blame the campaign, but a genuine performance change is rarely that abrupt. Far more often the tracking broke. WooCommerce conversion tracking is fragile to ordinary maintenance: a plugin or theme update changes the checkout flow, a caching plugin serves a cached thank-you page that never fires the purchase pixel, or a tracking plugin update quietly stops sending events. The campaign is fine; the receipts stopped arriving.

Layered on top is structural data loss. Cookie-consent rejection, ad blockers, and Safari and Brave privacy defences remove somewhere between 30 and 50 percent of conversions from client-side tracking, and ITP expires the click identifiers that longer attribution windows depend on. Google Ads enhanced conversions are meant to recover some of this, but they fail silently in roughly two-thirds of WooCommerce setups, so stores think they're covered when they aren't.

The diagnostic discipline is to separate real drops from reporting drops. Reconcile the platform's reported conversions against your actual WooCommerce orders for the same period: if the orders are there but the conversions aren't, the problem is measurement, and cutting budget would be the wrong move. Server-side tracking addresses the root cause by recording the purchase at the order hook regardless of browser behaviour, which is why durable ROAS reporting starts with where the conversion is captured.