Canonical from HTTPS to HTTP issue means that HTTPS page has a rel=canonical attribute that points to the HTTP page.
The importance of the issue
Search engines make all efforts to ensure website security, so applying the HTTPS protocol is currently highly preferable, though not required. The application of HTTPS is considered a good practice and the website’s positive ranking criteria.
When the HTTP protocol is applied, the Chrome browser sends an insecurity notification able to affect the user’s impression about your website and its conversion and search positioning.
The canonical attribute of the link tag forwards a search engine to a page with a similar or backup content you consider the main one. In its turn, the search engine defines the main version of the page. For this, it might consider or ignore the meaning of the canonical tag. As a rule, the canonical tag can be ignored when both pages’ contents differ significantly.
To put it simply, you notify the search engine that the main version of your page is applying the HTTP protocol instead of HTTPS.
How to check the issue
Using any browser is enough to check the issue. Open the source code of the flawed page. To do this, click the right mouse button at any spot of the page and choose “browse the code” option, or apply an online tool Codebeautify.
Find the link tag with the following rel=canonical attribute <link rel=”canonical” href=”http://site.com”>. Check the protocol specified in the href attribute.
How to fix this issue
Check the protocol specified in the href attribute to https.
Example: <link rel=”canonical” href=”https://site.com”>
Canonical settings are usually global, so their fixing requires changing the website plugin or template settings. If the issue is detected at separate pages, it can be fixed by setting the template or plugin for these specific pages.
Detect HTTPS pages with HTTP canonical
Crawl the website to collect all HTTPS pages that have HTTP canonicals