I have exactly got the same issue!
From May 22, my visitors’ numbers have gone from 30 a day to 5 max, sometimes 0.
I believe it is just because Google Analytics is not firing until the user accepts the cookies (terms & conditions bar at the bottom). I think one of my plugins (either Cookie Notice or Monster Insights) does not trigger Google Analytics by default and waits until the user accepts the cookies. There might be an option to change this behaviour in one of those plugins.
This is a bit of a rubbish behaviour TBH. Monster Insights gives a tutorial about how to set up GA to make it work, but I’m not sure it is for this behaviour: https://www.monsterinsights.com/docs/getting-started-with-the-eu-compliance-addon/