This error occurs when the page has a canonical to a different page. For example
The page URL is https://www.mysite.com/en/uk/somepage.html but the canonical tag on the page references a different URL. In this case it is pointing to the http version. These are two different pages and they must match.
<link rel="canonical" href="http://www.mysite.com/en/uk/somepage.html"/>
Common reasons for mismatched canonicals.
Canonical To HTTP or HTTPS version
Canonical to Trailing Slash
Canonial to Parameter