I'm working on a site that has recently seen a drop in search traffic. When digging through, we noticed that our latest content is not indexed. When I check some of the URLs in the Google Search Console for new content, the reason for the non-indexing will be "Duplicate non-canonical URL".
From there, I see several cases where, using the URL Verification Tool, the User-Declared Canonical URL displays a different URL (for a completely different and non-contiguous content than years ago). Most curiously, when using the "TEST LIVE LINK" button, the "user-declared canonical" displays the correct URL.
Why is the "user-declared canonical" tab different between "GOOGLE INDEX" and "LIVE TEST" in Google Search Console?