This issue arises when a URL is assigned different canonical tags in more than one location (such as within the HTML code and the HTTP headers), and these tags do not match each other.
Why is this important?
Conflicting canonical tags can cause search engines to disregard any canonical URL directives. This may lead to undesired indexing of duplicate pages that you prefer to remain excluded from search results.
What does the Optimization check?
This Optimization is triggered when any internal URL includes multiple mismatching canonical link elements. There might be one canonical link in the HTML and one in the HTTP header, or there could be two distinct canonical links in the HTML itself.
Note: Activating this Optimization will also activate the Optimization for:
Multiple canonical tags.
Examples that trigger this Optimization:
Take for example the following URL: https://example.com/page-a
This Optimization would trigger if this particular URL had divergent canonical declarations; examples include:
Two canonical tags in the HTML <head>, each different:
<!doctype html><html lang="en"><head> <title>Page Title</title> <link rel="canonical" href="https://example.com/page-a" /> ... <link rel="canonical" href="https://example.com/page-different" /></head><body>...</body></html>
OR one canonical tag in the HTML <head>:
<link rel="canonical" href="https://example.com/page-a" />
AND a different canonical declared in the HTTP header:
HTTP/... 200 OK...Link: <https://example.com/page-different>; rel="canonical"
How do you resolve this issue?
Identify the accurate canonical URL to be used, and ensure it is the sole reference across the site. Proceed by selecting a consistent method for assigning canonicals, such as exclusively through the HTML. Ensure that the canonical is set just once in every page template and adjust or eliminate any plugins causing discrepancies if needed. Consulting with a developer may be necessary to decide the best approach to streamline management for your website.