I noticed a penalization in google serp in my and many other websites. For everyone the date is the same: 17/18 gen.
I see the problem for some important sections of the site, but not the whole website has this problem. The traffic decreased about of 30% / day, some keywords on 1st position or only 1st page on google serp now are completely disappeard :(
I think it could be due to over-optimization (but is the same strategy used in past years, not any cloacking or doorway or other deprecated techniques)

Anyone with the same experience?
Which steps to check now?