Website suddenly dropped off

I have 3 nearly identical websites for 3 different local businesses in my area. I apply the same SEO strategies to all of them and it has been working fine up until last week. One of the websites dropped off suddenly Wednesday December 18 from the search while the other 2 are improving everyday. It went from 500 impressions a day to now 50 a day max. How can I find out what is going wrong this website and fix the issue? Semrush isn't telling me anything conclusive.