The issue highlighted here is that an AMP Page URL includes a canonical reference to a noindex URL.
Why is this important?
For AMP HTML pages to be validated, a canonical link to the equivalent standard page is a must-have, or a self-reference if such equivalent does not exist. If this canonical points to a noindex URL, it becomes probable that search engines will not index the AMP version.
Sending mixed signals to search engines through a noindexed canonical reference inadvertently reduces the likelihood of the AMP page appearing in search results.
What does the Optimization check?
The Optimization activates for any AMP Page URL where a canonical link is directed to a noindex URL.
Examples that trigger this Optimization
Take, for example, the AMP Page URL: https://example.com/amp/page-1/
You would witness the Optimization being activated if this URL included a canonical link like the following:
<!doctype html><html amp> <head> <meta charset="utf-8"> <title>Example Title</title> <link rel="canonical" href="https://example.com/pages/page-1/" /> ... </head> ...</html>
and if this canonical URL has a noindex directive in the <head> or as an HTTP header:
When meta noindex exists in <head>:
<!doctype html><html lang="en"> <head> <title>Demo</title> <meta name="robots" content="noindex,nofollow"> ... </head> <body>...</body></html>
Or indicated via HTTP header:
HTTP/... 200 OK...X-Robots-Tag: noindex
How do you resolve this issue?
AMP page canonicals need to refer to indexable URLs.
To resolve the inconsistency, it’s necessary to update the canonical link on the AMP page so it accurately points to the corresponding non-AMP page, while also ensuring this target page is not marked noindex.
Furthermore, the non-AMP version should have a self-referencing canonical in the following manner:
For the URL: https://example.com/pages/page-1/
This page should self-reference and also reference its AMP counterpart:
<link rel="amphtml" href="https://example.com/amp/page-1/"><link rel="canonical" href="https://example.com/pages/page-1/" />
The AMP page, in turn, should maintain a canonical link that reverts back to https://example.com/pages/page-1/
<link rel="canonical" href="https://example.com/pages/page-1/" />