A powerful update to Google algorithm happened in Mar, 2017 which seemed to have affected majority of websites which are employing black hat techniques.
So, how do you know if you are affected.
Lost google rankings
Drop in Alexa - yes alexa is not always about traffic
So to recover, all low profile backlinks disvow them, then add fresh content preferably over 1000 words, don't stuff keywords only 2-3 times in
one content is more than enough, re-write meta tags, build manual links about
50 of them. Your rankings is sure to improve in few weeks time.