Why you have duplicate GA4 tags firing
If your pageviews doubled overnight and engagement collapsed, you probably have GA4 installed twice. It is one of the most common and most data-wrecking setups there is.
How it happens
- GA4 is hard-coded in the theme and added again in GTM.
- A plugin or a Shopify channel installs it, and someone adds it manually too.
- A site migration left the old tag in place alongside the new one.
What it does to your data
Pageviews and sessions inflate, engagement and bounce metrics go haywire, and conversions can double, the same problem as duplicate conversions.
How to find and fix it
Use the Google Tag Assistant or your browser's network tab to count how many GA4 (collect) requests fire on one pageview, more than one means a duplicate. Then remove the extra install so GA4 loads exactly once, ideally only through GTM. A free check flags a double install instantly.
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