Description
The two causes are RDP plug-ins and UDP usage under certain conditions.
Solution for RDP plug-ins
Solution for UDP usage
There's an option in RDM to disable UDP usage.
1. Open Remote Desktop Manager as an administrator.
The research in this solution hint that this is caused only when going through a VPN, others mention that it occurs only on Windows 8 paired with a Gateway server, but it has worked for many of our users.
It requires a registry change, so all the usual warnings and caveats apply here, back it up first! Consult this Microsoft support article for more information.
The fix is to disable UDP on the client workstation:
1. Navigate to HKLM\SOFTWARE\Policies\Microsoft\Windows NT\Terminal Services\Client.
2. Create a DWORD named fClientDisableUDP and assign it a value of 1.