Google kept the details of the changes made secret, so various theories about the update arose all over the internet, but no theory was clearly proven. A large number of theories contradicted each other. Most relied on a very limited number of sites even the more systematic ones were based on a very small sample of sites and tests.
Some of the more common theories that came up regarding the update:
1. This update negatively affects sites that have many pages with certain word combinations (for example, sites targeting <profession> + <city> keywords). This is the most common theory regarding the update.
2. The update has a negative effect on sites with a large amount of advertisements.
This theory referred to the update as an extension of the Fred update. It was based on a sample of 44 sites, all containing a large amounts of advertisements.
The same group of sites also included mainly affiliate and e-commerce sites, a fact that caused suspicion the update was aimed at sites of this type.
3. Another theory - The update has a negative effect on sites that have obtained EDU links using payment / advertising / cooperation, more specifically - obtaining links from academic sites by funding student scholarships (and receiving links in exchange).
In this interview [https://diggitymarketing.com/interview-with-luqman-khan-of-10beasts/], a man claimed that removing these links solved the problem at those specific websites.
The Internet has been filled with many other theories. The bottom line is that if this update has a negative effect on your website, our recommendation is to make sure your website meets all the known SEO rules and parameters - links, content, duplicate content and other adjustments.
According to Google's statement – settling for one single change won’t help. You have to ensure a proper level of SEO, addressing the different aspects.