Why does GA4 double-count SPA page views only when visitors use the browser Back or Forward button?

It’s usually two page-view setups reacting to the same browser-history navigation. In an SPA, Back/Forward restores a history entry, and GA4 enhanced measurement can send a page_view for that history change. If GTM or your app also sends a virtual page_view on that event, you’ll get two. The fact that it only shows up on Back/Forward usually means the manual handler is attached to popstate or history changes while your normal route navigation has some extra guard. Pick one owner for SPA page views: either GA4’s enhanced measurement for browser-history changes, or a GTM/manual page_view setup. Don’t run both. Then use GTM Preview and GA4 DebugView to confirm one page_view per navigation and that page_location and page_referrer look right. Also check that a Google tag/config tag isn’t automatically sending a page view in addition to your explicit event.