I’m a WordPress developer (at the moment). We use the free CDN product. We use a WordPress plugin called “WPS Hide Login”. Attempts to access password protected posts generates 404 errors on redirect from the password form to the protected content. The password form has “Cache-Control” → “no-store”.
Turning off Railgun allows form submit redirection to protected content.
This is more a notification about the problem than a request for help, although it would be nice to have both the plugin and Railgun active.