RDP8.1 client disconnects/reconnects randomly about every 2 minutes when connecting a RDP8.0 (WIn 2012) server

I have not been able to reproduce this in a LAN-environment, only in a WAN (remote) environment (probably related to higher latency)

Things tested that DO NOT resolve this:
- With gateway, reconnects happen more requent, probably due to proxying
- UDP on or off, no resolve
- FW tcp/udp timeouts doubled, no resolve
- keep alive settings on or off, no resolve
- Tested all different network-settings in the client (detect auto, WAN, LAN, broadband, etc. settings), no resolve
- RDS Server is on Hyper-V, moved it to another host with different teaming/physical NICs (and thus drivers), no resolve
- Tested with the Hyper-V under heavy load or almost 0% load, no resolve
- Average ping (remote) from client to gateway: 50 ms
- Average ping (remote) from client directly to RDS Server: 50 ms
- Tested fwith a client from a different location (and different internet provider), no resolve
- Completely updated RDS Server with all updates, no resolve

Things tested that DO resolve this (thusfar) getting 0 disconnects during several hours on end:
- Upgrading the RDS Server to 2012 R2 (thereby replacing server-side RDP8.0 to RDP8.1)
- Using client RDP8.0 at the client-side

It looks to me I ran into a RDP8.1 client bug here...

Is there anything else I could try to resolve this without having to upgrade the server (not very convenient because of software-support) or downgrading the client to RDP8.0 (not very convenient either if the client is Windows 8.1 < mostly in our case here) ?