About 3 hours back, I noticed about 20% are no where to be found. A huge drop from page 1-2 and there are no longer in page 50 also. The sites are still indexed. All of the sites are built using various services rotated monthly so backlinks are not a problem as they are a lot of links as I checked.
So what I can gather;
1. google is doing manual review on top pages and if they look ugly and thin they will be flagged and gone.
2. I still have sites which ranked to top position for EMD today and they will receive the initial boost and will drop if no updates done.
3. I checked all the sites which is still ranking and found one thing in common. They not only write good quality unique content, they have nice images to complement with graphs, videos and also facebook pages and opt in. So google is looking at overall site and no longer just backlinks and unique content. Some sites have poor lousy or little content but they interact a lot with users in terms of comments and still rank very high in Google.
Gone are the days you can build EMD sites + articles + backlinks and earn a good income with Google. Authority sites with actual work put in will give you the blessings of Google and ranked highly.
So today if your site is using same theme, thin sites with MFA, 100% you will be flagged, just a matter of time.
Just my 2 cents worth.