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:
The Hint MAY also trigger if you have invalid HTML elements which break the <head>, as this can mean that the <body> starts early, and the canonical tag ends up in there.
How do you resolve this issue?
This Hint is marked 'Critical' as it represents a fundamentally breaking issue, which may have a serious adverse impact upon organic search traffic. It is strongly recommended that Critical issues are dealt with as a matter of high priority.
Typically, this comes from an instance where the <head> gets broken. When Googlebot parses your HTML, the canonical tag is moved to the body. Check to see if either of these Hints are also triggered:
If this is the case, then resolving these issues first may also resolve the canonical problem.
If either of these 2 Hints is not triggered, however, you'll need to do some more digging to investigate the issue. It would then indicate 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.