Native RDP sessions not connecting (13.0 HF2)

I'm actually investigating a similar issue (also v13 HF2, also native RDP resource). Actually in my case (on an F5 VE), I narrowed it down to the native RDP resource not working when there are multiple tmm instances active. Check in tmsh. show /sys tmm-info. If I limit the number of CPUs to one, it does effectively work. When I increase the CPUs to 2, the RDP resource will stop working. The thing where it's different is that, in my case the backend server (3389) is never contacted whenever it won't work. I verified with tcpdump. There's not a single SYN that gets sent. Could it be that you actually have the same issue using the native RDP resource and that your "connection refused" messages in Windows only occur using the activeX RDP resource?