How to remove the brakes on the thin client on the pages loaded with graphics?

Question

RDP

We have a client-server architecture raised on wtware 5.4.8
We have a server in the DC, where we connect via a VPN tunnel at a guaranteed speed of at least 60 Mbps
No more than 15 people are sitting at the same time, the channel is utilized by no more than 15%
The return from the DC is guaranteed 1 Gbps
Clients receive connection parameters to the server via tftp from wtware 5.4.8
Clients connect to Windows 2008R2
When connecting from the same network via RDP client windows or remmina, there is no
problem. .ua
Everything is cheerfully loaded with squares and stripes
By reducing the color to 16 bits and reducing the resolution to 1368 * 768, the problem decreases, but does not go away
Changing different types of drivers and other dances with tambourines do not solve the problem
Question: how to remove artifacts and cell-by-cell loading?
Yes, I understand that these are jokes of the RDP protocol, but the users themselves do not know such words and want the blood of IT people