Referrer always blank

Sounds like a similar problem to the one I had.
See this thread https://www.ads-software.com/support/topic/log-report-page-broken

Take a look at the log-page source code – if the referrer is in page source, some HTML is preventing the browser displaying the referrer information.

This article may help fix this and similar problems
https://tech.graphicline.co.za/404-redirected-log-reports-broken/