Make sure that you SEO is good and that you have a good sitemap. What plugin(s) are you using for your sites SEO? Also did you consider the fact that you could have just lost some regular visitors? Not all websites get a magical amount of views every day.
In Yoast SEO, most of my posts get good SEO score and I have also uploaded my sitemap to google wheneven I update my site. And I am currently using both Yoast SEO and All in one SEO plugins