Canonical outside of head
This means that the URL in question has a canonical element specified in the HTML, but outside of the <head>.
Why is this important?
If a canonical is specified outside of the <head>, it will be completely ignored by search engines.
Ultimately this means that whatever you had hoped to accomplish with this rel=canonical will not come to fruition.
What does the Hint check?
This Hint will trigger for any internal URL which contains a canonical in the HTML, yet outside of the <head> area.
Examples that trigger this Hint:
Consider the URL: https://example.com/
The Hint would trigger for this URL if it had a canonical tag that was anywhere outside of the <head>, for example:
How do you resolve this issue?
If this Hint triggers, it indicates a configuration issue on the URL in question, which is likely due to an issue with a page template or plugin which is putting the canonical in the wrong place. The canonical tag will need to be removed from the <body> (and replaced in the <head>), so you may require developer assistance.