Two additional issues have been created to track the authentication parts of this problem.
I have submitted a fix for AS7-1861 to cover the scenrio where keep alive connections are shared by multiple clients, however AS7-1856 is still outstanding as I am unable to reproduce that failure.
Are you getting anything logged by Apache to report why it is reporting that error code?
I am using CR1b. Is this still a bug? When I try to use Proxy and ProxyReverse to front with Apache, I get the loading spinning wheel and it goes nowhere.