Source Address Persistence issue

Are your clients behind a proxy? If you have long-running sessions then you want to maintain persistence but it could be that all of your clients are only matching a single persistence record. You can check by looking at your persistence records. Do you have Match Across Services set in your persistence profile? I would expect that new connections will be loadbalanced across the servers, even if those sessions are long-running.

It could be that you would be better off assigning an HTTP and OneConnect profile and using cookie persistence instead. To improve your monitor, use the HTTP monitor and set the port to one on which you know the web server is running.