Penalty. Probably algorithmic if you got no mail. This can happen any time, no need for a google update. My own rankings are jumping around for months already.
If you want to try to revive and keep it for long term:
Time to clear up your backlink profile, might take some months until you rank again.
If you want to revive it now and afterwards loose it forever:
Blast it with backlinks.
Anyways, be prepared that it will never rank like before again in a looong time. And you don't need to hurry, at this point there is nothing you can do in short term, they got you.
After reading your posts I think you must be new to SEO. 20k traffic is a lot, you probably were just lucky that you ranked long for such competitive keywords, sometimes google just does not comprehensible things. If you bought backlinks here on blackhatworld(or anywere) to achieve this, now you may pay the price for it.
This is the single most retarded thing I’ve ever read on BHW. Google is not recording metrics from your social pages.
Now if it’s a local business and you stream in reviews on your site that’s a different story. But for a movie streaming website Google is not ranking based on “social retention”.
There are public case studies on this which say that google does to some extend in some way. I read one where twitter tweets of popular twitter pages increased ranking pretty fast, especially in short term. Unbelievable how you can be so convinced about your statements in such a complex topic like seo.
It's 2019, Google probably uses EVERYTHING what it can somehow get, to calculate the rankings.
