Canonical URL changes when JavaScript runs

What this means

The rel=canonical in the server's HTML does not match the one present after JavaScript executes. Google may consolidate on either target depending on which pass it acts upon, so this is a live indexing hazard: the wrong version can deindex the page or fold it into an unrelated URL.

How to fix it

Declare one canonical, server-side, in the initial HTML response. Never inject, rewrite or remove rel=canonical from client-side JavaScript.

Fix effort

This check needs a developer fix: it turns on a routing, hosting or infrastructure decision that no automatic edit can make safely.

Authoritative source

https://developers.google.com/search/docs/crawling-indexing/consolidate-duplicate-urls