I am trying to understand what happened to one of my sites one month ago. On October 28th it lost 90% of all traffic, and it's been steady at that new low level ever since. The most obvious reason for the drop is that the traffic used to come from about 30,000 various long-tail KWs per month, and now it's down to only 1,500.
However, when I check those keywords that still bring traffic, they are all consistently in positions #1,2 and 3 where they used to be anywhere between 3 and 10 before. Many of the old most popular KSw still bring traffic and are positioned even better than before, but most long tail ones are gone. It's like there has been an overnight hollowing-out of thousands of rare and perhaps very long-tail KWs that only brought 2-3 visits in the entire month. I sometimes can find the old KWs at the very end of the results, sometimes nowhere at all.
I've discovered some spam in UGC (not terrible but rather pesky, visible and completely off topic - it was the election time in US and it was political spam) and submitted a reconsideration request after I deleted it but received a response saying "No manual action". I thought perhaps that political spam had skewed Google's perception of the site's theme. Anyway, whatever it was, it was algorithmic.
I can't find any date reference to an update around October 28th, so it seems like some "normal" re-ranking. I put "normal" in quotes because losing 90% of traffic sure feels like a penalty but Google says it's not.
Would anyone have an idea on how to start digging out of this hole? Has it ever happened to you? How would you diagnose a sudden improvement in rankings of some KWs while the rest is completely gone?
Thanks for all your ideas and comments!