The author's views are entirely his or her own (excluding the unlikely event of hypnosis) and may not always reflect the views of Moz.
Last year, the team at Homeday — one of the leading property tech companies in Germany — made the decision to migrate to a new content management system (CMS). The goals of the migration were, among other things, increased page speed and creating a state-of-the-art, future-proof website with all the necessary features. One of the main motivators for the migration was to enable content editors to work more freely in creating pages without the help of developers.
After evaluating several CMS options, we decided on Contentful for its modern technology stack, with a superior experience for both editors and developers. From a technical viewpoint, Contentful, as a headless CMS, allows us to choose which rendering strategy we want to use.
We’re currently carrying out the migration in several stages, or waves, to reduce the risk of problems that have a large-scale negative impact. During the first wave, we encountered an issue with our cookie consent, which led to a visibility loss of almost 22% within five days. In this article I'll describe the problems we were facing during this first migration wave and how we resolved them.
For the first test-wave we chose 10 SEO pages with high traffic but low conversion rates. We established an infrastructure for reporting and monitoring those 10 pages:
After a comprehensive planning and testing phase, we migrated the first 10 SEO pages to the new CMS in December 2021. Although several challenges occurred during the testing phase (increased loading times, bigger HTML Document Object Model, etc.) we decided to go live as we didn't see big blocker and we wanted to migrate the first testwave before christmas.
Very excited about achieving the first step of the migration, we took a look at the performance of the migrated pages on the next day.
What we saw next really didn't please us.
Overnight, the visibility of tracked keywords for the migrated pages reduced from 62.35% to 53.59% — we lost 8.76% of visibility in one day!
As a result of this steep drop in rankings, we conducted another extensive round of testing. Among other things we tested for coverage/ indexing issues, if all meta tags were included, structured data, internal links, page speed and mobile friendliness.
All the articles had a cache date after the migration and the content was fully indexed and being read by Google. Moreover, we could exclude several migration risk factors (change of URLs, content, meta tags, layout, etc.) as sources of error, as there hasn't been any changes.
Visibility of our tracked keywords suffered another drop to 40.60% over the next few days, making it a total drop of almost 22% within five days. This was also clearly shown in comparison to the competition of the tracked keywords (here "estimated traffic"), but the visibility looked analogous.
We had to identify issues as quickly as possible and do quick bug-fixing and minimize more negative effects and traffic drops. We finally got the first real hint of which technical reason could be the cause when one of our tools showed us that the number of pages with high external linking, as well as the number of pages with maximum content size, went up. It is important that pages don't exceed the maximum content size as pages with a very large amount of body content may not be fully indexed. Regarding the high external linking it is important that all external links are trustworthy and relevant for users. It was suspicious that the number of external links went up just like this.
Both metrics were disproportionately high compared to the number of pages we migrated. But why?
After checking which external links had been added to the migrated pages, we saw that Google was reading and indexing the cookie consent form for all migrated pages. We performed a site search, checking for the content of the cookie consent, and saw our theory confirmed:
This led to several problems:
But why was this happening? According to our service provider, Cookiebot, search engine crawlers access websites simulating a full consent. Hence, they gain access to all content and copy from the cookie consent banners are not indexed by the crawler.
So why wasn't this the case for the migrated pages? We crawled and rendered the pages with different user agents, but still couldn't find a trace of the Cookiebot in the source code.
To validate that Google was reading the copy from the cookie consent banner, we used the URL inspection tool of Google Search Console. We compared the DOM of a migrated page with the DOM of a non-migrated page. Within the DOM of a migrated page, we finally found the cookie consent content:
It took a while to find it because we thought the second file was just a pre-requirement for the first one. We determined that simply removing the loaded cd.js file would be the solution.
The day we deleted the file, our keyword visibility was at 41.70%, which was still 21% lower than pre-migration.
However, the day after deleting the file, our visibility increased to 50.77%, and the next day it was almost back to normal at 60.11%. The estimated traffic behaved similarly. What a relief!
I can imagine that many SEOs have dealt with tiny issues like this. It seems trivial, but led to a significant drop in visibility and traffic during the migration. This is why I suggest migrating in waves and blocking enough time for investigating technical errors before and after the migration. Moreover, keeping a close look at the site's performance within the weeks after the migration is crucial. These are definitely my key takeaways from this migration wave. We just completed the second migration wave in the beginning of May 2022 and I can state that so far no major bugs appeared. We’ll have two more waves and complete the migration hopefully successfully by the end of June 2022.
The performance of the migrated pages is almost back to normal now, and we will continue with the next wave.