Canonical points to a URL that is Error (5XX)

This means that the URL in question has a canonical element whereby the canonical URL itself resolved in an error (5XX).

Why is this important?

The problem with this error is twofold:

1. The 5XX status code represents and internal server error, which means that the server was unable to process the HTTP request and serve the content.
2. Since the canonical URL errored, Sitebulb was not able to confirm that the canonical was well defined (i.e. pointing to a Success (200) URL that is indexable and crawlable).

What does the Hint check?

This Hint will trigger for any internal URL which contains a canonical link element where the canonical URL returned a 5XX error when Sitebulb tried to crawl it.

Examples that trigger this Hint:

Consider the URL: https://example.com/page-a

The Hint would trigger for this URL if it had a canonical URL pointing at another internal page,

<link rel="canonical" href="https://example.com/page-b" />

where this canonical URL https://example/com/page-b responds with a 5XX error:

HTTP/... 500 Internal Server Error

...

How do you resolve this issue?

Since the problem is twofold, the solution is also twofold, and both solutions are affected by the scale of the problem.

1. If you are seeing lots of internal pages return 5XX consistently, it implies there is some sort of hardware problem, and the best course of action is to speak to your hosting provider and get them to investigate the issue further. If this 5XX error was a one-off, and responds correctly when you view the page in the browser, it is probably safe to ignore for the time being - but keep an eye out for more 5XX errors in future audits.
2. Assuming you are dealing with only one or two error URLs, you need to manually check them in your browser to confirm there are no other issues with the canonical configuration. Since this URL is the canonical for another, you need to make sure it responds with a 200 status and is indexable and crawlable.