Drop in Position. Is it because of the change in Algorithm?

I have been successfully doing SEO for many of my clients. All were very happy with the position achieved on main search engines. However, this week, they complained about the drop in position within Google SERP. A few of the sites faced a drastic drop. If spoken about keywords, each client had all range of keywords, be it high-end competitive ones or low-end non competitive ones. Many of the fellow SEO friends also found a decrease in position for their client’s site. So, I thought that Google is modifying its algorithm. What do you think? Do you think my guess is accurate?

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