Is your website HTTPS? Referrer isn't passed from HTTPS to a non secure site, which is what Google Analytics normally bases its reports on (referrer). From the HTTP spec: https://tools.ietf.org/html/rfc7231#section-5.5.2
Looking at your ads, only 1 out of 4 ads are HTTPS. For example, the first ad on the list (which is one of your active ads) is HTTP (not HTTPS), even if your server redirects to HTTPS, it doesn't matter because the HTTP spec doesn't pass referrer info along to the first hop because it's not HTTPS.