Why do HTTPS migrations break your canonicalization?

What really happens during an HTTPS migration?

When you switch your site to HTTPS, Google must reassess each URL to determine which version should be indexed. In theory, your 301 redirects clearly indicate that http://example.com becomes https://example.com.

The problem? Google's algorithms do not just blindly follow your redirects. They also analyze your internal links, sitemaps, external backlinks, canonical tags, and Search Console data. When these signals diverge, the engine must decide.

Why does Google mention failing algorithms?

Mueller admits that there are cases where the algorithms misinterpret the data. This is not a one-off bug that can be fixed with a minor adjustment. It is a structural limitation of the mass automated processing of migrations.

In practice, you could set up all the recommended best practices and still observe indexing fluctuations for weeks. Your old HTTP URLs may continue to appear in the index, or worse, both versions coexist.

What conflicting signals disrupt canonicalization?

The engine crosses a dozen different sources. A forgotten internal link to the old HTTP version carries less weight than a 301 redirect, but if you have 500 of them, it muddles the waters.

External backlinks still pointing to HTTP also create confusion. Google must decide whether to follow the redirect or consider the original URL as still relevant because it is still receiving link juice.

• 301 redirects are just one signal among others, not an absolute instruction
• The internal linking must be 100% consistent on the day of migration
• XML sitemaps should exclusively list the final HTTPS URLs
• Canonical tags in the HTML code must point to HTTPS
• The preferred domain declaration in Search Console must be updated

Does this official recognition change anything on the ground?

Not really. Experienced SEOs have known for years that HTTPS migrations are unpredictable. What is new is that Google admits it publicly instead of consistently referring to a checklist of best practices.

This primarily confirms that a technically perfect HTTPS migration can still derail. You are not necessarily at fault if indexing takes six weeks to stabilize, even with clean redirects and a flawless internal linking structure.

When do we observe the most problems?

Large sites with hundreds of thousands of URLs are particularly exposed. Google crawls in small chunks, gradually discovering the redirects, and takes time to update its index.

Sites with many historical backlinks to HTTP also pose issues. If 80% of your link profile still points to the old URLs, Google hesitates to mass canonicalize to HTTPS at once. [To be verified]: it is not clear exactly what ratio of HTTP/HTTPS backlinks triggers this behavior.

Should anything be done differently now?

No, the fundamentals remain the same. Redirect everything with 301, fix 100% of the internal links before migration, submit a clean HTTPS sitemap, declare the new version in Search Console.

What changes is your level of expectation. Don’t panic if indexing takes four to six weeks to stabilize completely. Keep a close watch on Search Console, but do not overreact to every temporary fluctuation. If after two months you still see significant HTTP URLs indexed, then you have a real technical issue to investigate.

What should be prioritized during an HTTPS migration?

The internal linking is your most controllable lever. Even before launching the migration, crawl your site with Screaming Frog or Oncrawl to identify all hard links to HTTP in your templates, menus, footers, breadcrumb trails.

Fix these links beforehand. Do not rely on redirects to compensate for internal linking that points to the old URLs. Every HTTP internal link you leave behind sends conflicting signals to Google's algorithms.

How to monitor canonicalization progress post-migration?

In Search Console, monitor the number of indexed URLs on both versions of the domain (HTTP and HTTPS). You should see the HTTP URLs progressively decrease while the HTTPS URLs increase.

Also use queries like site:http://yourdomain.com and site:https://yourdomain.com directly in Google. If after a month you still see 30% of your pages in HTTP in the results, something is wrong with your canonicalization signals.

What critical errors consistently cause issues?

Leaving both versions accessible without redirection is a guaranteed disaster. Google will index both, your PageRank will be diluted, and you will have massive duplicate content.

Another classic pitfall is only redirecting the homepage and leaving internal pages accessible in HTTP. Redirect URL by URL, not just the root domain. And ensure that your SSL certificates cover all your subdomains if you use any.

• Crawl the site before migration to identify all HTTP internal links to fix
• Implement permanent 301 redirects for each URL individually
• Submit a new XML sitemap containing exclusively the HTTPS URLs
• Declare HTTPS ownership in Search Console and set the preferred version
• Check that all canonical tags point to HTTPS URLs
• Monitor indexing evolution daily for the first six weeks