If you connect your IGEL Linux based Thin Clients thru a bad WAN connection it may happen that the session drops for the user.
Before you try any other optimizations try to disable the timeout for the RDS session by enabling the setting System->Registry->rdp->winconnect->disable-timeout
If this is not working try the RDP legacy mode or disabling IPV6, just search in this FAQ to find the related articles.
You can also try to reduce the communicationd data between the client and your infrastructure by:
1) Reducing the resolution/color depth
2) Disabling all not required features like printer/drive/serial port/clipboard/smart card/Audio mappings (as alternative you can enable the Audio compression or reduce the Audio quality for RDS too.
Attention: If you enable the RDP legacy mode and the WAN connection is really worse you can expierence a freezing mouse or that some mouse / text inputs are very slow or not working in the session.