In March 2019, a friend of mine lost 70% of his website traffic in one day. A Google SERP algorithm update hit him.
One of the biggest problems was that his content was not unique anymore. For 5+ years, he hired experts in his domain to write thousands of high-quality blog posts.
However, silently, theses articles were being copied by malicious or dishonest website owners.
To get his rankings back, he had to:
fill in the copyright removal form Google provides in the Search Console.
contact
He first needed to find all content thefts. That's where I helped. I worked on a script which:
scanned his website
looked for thefts for each of the blog posts and compared the two texts.
exported a list of potential thefts.
It was slow and incomplete. But It helped my friend a lot. Using the list, he got rid of almost all content thefts. He also got a significant part of his ranking backs.