Just a heads up… was searching around for this error message and discovered this possible solution. It doesn’t look like it is a W3TC problem:
Just in case if you are here but your referrer policy looks fine but your URL page contains google-ad-words or something social, then ad-blocker might be the culprit. try disabling it.
Some other advice…it could be an incompatibility with your browser.
Chrome (desktop/mobile): need at least v61 for full support (Min: v56).
Firefox (desktop/mobile): need at least v52 for full support (Min: v50).
Internet Explorer/ Microsoft Edge + mobile: Not supported at all.
Safari (desktop and mobile): Not supported at all.
Opera (desktop and mobile): need at least v48
Samsung Internet Browser: basic support in v6.0
I tested w3tc’s Referrer-Policy setting in both the latest Chrome and Firefox. Both work perfectly for every directive (and with ADB+ enabled ;P ).