"Duplicate, Google chose different canonical than user"

Question

Most of the pages on my site seem to have indexed just fine. However, when I do an inspection for a certain page on my site, let's say it's http://www.example.com/importantpage.html, it shows "URL is not on Google". The reason is listed as "Duplicate, Google chose different canonical than user". However, below that it shows

User-declared Canonical: http://www.example.com/importantpage.html

Google Selected Canonical: N/A

How did "Google choose a different canonical" but the Google Selected canonical is N/A?

---

In the head of importantpage.html I have the following tag defined:

<link rel="canonical" href="http://www.example.com/importantpage.html" />

I also have this entry in the sitemap:

<url>
    <loc>http://www.example.com/importantpage.html</loc>
    <lastmod>2018-10-01</lastmod>
    <priority>1</priority>
</url>

I also have a tag defined:

    gtag('config', '<property id>', {
        'page_title' : 'importantpage.html',
        'page_path': '/importantpage.html'
    });

The only thing I can think of that is different for this page is that we have a domain that forwards directly to it (eg, www.1.example -> www.example.com/importantpage.html). But since I'm defining the canonical I don't see how this would cause it, but it does seem like a likely culprit. If so, how would I fix it?

Things to note:

• We have no HTTPS
• I am rewriting everything to www. in .htaccess.
• We have multiple domains that redirect (301) to www.example.com
• We have one domain that forwards to www.example.com/importantpage.html (as mentioned above)

---

.htaccess

RewriteEngine on
RewriteCond %{HTTP_HOST} ^example.com [NC]
RewriteRule ^(.*)$ http://www.example.com/$1 [L,R=301,NC]

Answer 1

If your domain redirects are permanent then Google should only be indexing the final page.

If you are marking the page as canonical then it should be accepting that as the page to index.

But as Google believes that you have duplicate page...

"Duplicate, Google chose different canonical than user"

(and it's probably a duplicate instance of that page) then that is what you should focus on removing.

I'd use a SEO site link check tool to list all links being created by your site, and find the possible duplicate(s).

Without seeing the site, and the htaccess file I couldn't tell you if your redirects are correct, but finding the duplicate will most likely tell you what is causing it.