Whenever user authentication requests from a remote domain reach the ProxySG appliance, it resets the schannel because Domain Controllers in that domain are not reachable by the Domain Controller that is local to the ProxySG.
Users may experience authentication failures or authentication prompts when this occurs. This is because the ProxySG appliance is continually resetting the schannel (0xC000005E - STATUS_NO_LOGON_SERVER) when the Domain Controllers in the remote domain are not reachable by the local Domain Controller connected to ProxySG appliance. This issue has been reported in SGOS versions prior to 18.104.22.168
This behavior is caused by bug # 232071. A firmware upgrade to SGOS version 22.214.171.124 (or above) is required.