Full Answer

An Unassigned traffic spike in GA4 is a diagnostic signal, not a mystery — it points to a specific technical failure in your campaign tracking chain that can be systematically identified and fixed.

GA4's channel grouping logic assigns every session to a channel based on available attribution data. When a session arrives with no utm_source, no utm_medium, no referrer header, and no recognised click identifier, GA4 has no basis for classification and defaults to Unassigned. A sudden increase in this channel means something recently changed in how traffic reaches your WooCommerce store.

The investigation starts with timing. Identify when the Unassigned spike began — ideally to the day — and cross-reference against infrastructure changes. The most frequent causes fall into three categories. First, redirect changes: a new htaccess rule, a WordPress permalink update, or a plugin-generated redirect that strips query parameters during the 301 or 302 hop. Second, CDN or caching layer updates: services like Cloudflare or WP Engine's caching may strip or rewrite query strings to optimise cache hit rates, inadvertently removing UTM parameters. Third, URL shortener changes: switching from a premium shortener that preserves query strings to a free tier that truncates them.

To diagnose, test a full campaign URL through every step of the delivery chain. Use an incognito browser, click the link, and watch the address bar through each redirect. If parameters vanish at any hop, you have identified the stripping point.