Authentication server configuration in Standard license is not persistent on reboot in Citrix Gateway. Users get an empty page with an error (just as when your content-switching virtual server does not have a policy bound and no default vServer).
Note: Standard edition license does not have AAA feature support, but creating a non-addressable authentication server is allowed. However this AAA virtual server is removed from the config on reboot. Authentication profile (bound to the Gateway vServer, if any) will be pointing to a non-existing AAA virtual server.