Canonical URL has no incoming internal links
This means that the URL in question has the target canonical URL for another internal URL, but has no incoming links (other than the canonical link element).
Why is this important?
If a URL has no incoming internal links, this means it is not really part of the overall website structure, in the sense that users could not navigate to it. Similarly, it is not being assigned link equity/value in the traditional sense.
Since it has no internal links, the Sitebulb crawler will have only found it through the canonical link element. Since it is a canonical URL, search engines are getting the message that it is a 'preferred URL for indexing'. If you want a URL to be indexed, you presumably also want it to rank well, so you would want to be directing at least some internal links at it.
Following this logic, it is highly likely that if this Hint triggers, it's because of some sort of unintentional mis-configuration on the website. And if it is intentional, you should probably change it.
What does the Hint check?
This Hint will trigger for any internal URL that has no incoming internal links, and is listed as the canonical URL on another internal URL.
Examples that trigger this Hint:
Consider the URL: https://example.com/page-a
This URL is canonicalized to another internal page,
where this canonical URLhttps://example/com/page-b has no incoming links from any internal URLs.
The Hint would trigger for this URL https://example/com/page-b
How do you resolve this issue?
The logical assumption in this scenario is that the URL in question has been accidentally left out of the main site architecture. As such, the solution to this issue is to arrange for the URL to be included in the site architecture, so that it has internal links from at least 1 other internal URL.
Issues like this will typically need to be resolved on a case by case basis.