Here is one glimmer of hope or interest. When I login as another user and then log out. Clear Website Cacheing on the browser/and Joomla site and refresh browser I am able to complete the form without error. I can also complete the form without error without any clearing of cacheing. I find this interesting that I can complete the form without error after logging in then logging out, but no other time. Do you see any connection in this or a cause?
Just sounds like for whatever reason Joomla is not creating your session or your session cookie is pointing to a non-existing session. This won't just break CB CSRF protection. Anything relying on sessions would fail in this case. I've no idea what causes it. It could just be server configuration issues with PHP, but I don't know. I would need a test environment where this can be reliably reproduced so I can add layers of debug code to trace what's going wrong. So far I have not been able to create such an environment nor has anyone been able to provide one as I cannot do this debugging on a live install with active users using it. The biggest issue is being able to reliably reproduce. It happening randomly doesn't really allow me to track down the cause.