RDC Connection gives blank screen on Mac when using IPSEC tunnel

Hi all,

Have the following issue. We run IPSEC tunnels from remote offices to the main office over fibre. All staff have a desktop in the office which they access via the IPSEC Tunnel. The staff who are using a windows laptop or desktop to run the Remote desktop do not experience any issues connecting to their office desktops via the IPSEC tunnels. However staff who are using Macbooks have the following issue. When they connect via the IPSEC tunnel, the remote desktop app connects, however the screen is blank. If they connect using a mapped port directly into the desktop via the router and do not use the tunnel the App works fine and they are able to do their work without any issues. We then changed the desktop RDC to use XDDM instead of WDDM to see if this will make a difference. Doing this, allows for the desktop to show on the Mac, however it still, every now and then, bring up a black screen. After a while you are able to see the screen again. 

We are obviously trying to not use the port forward option for security reasons.

Any idea why we are having this issue with the mac users? Are there better RDC software than the normal one on the app store. I have been unable to find anything useful on the net.

Thanks

Bernard