X-Pilot works fine on ground, but disconnects when airborne

I have a networked X-Plane 11 setup with Master running X-Plane in background, but also running Air Manager panels and X-Pilot. My Slave PC runs a separate copy of X-Plane 11 with the X-Pilot Plugin and I can see all the other aircraft on my three monitors and communicate with ATC perfectly whilst on the ground. However, as soon as I get airborne the X-Pilot connections drops every few seconds with the error message that my FPS are less than 20. In fact the fps are 25 - 35 constantly on the external visuals and over 75 on the underlying Master. My internet connection is an average of 20 mbs, so I am at loss to know why this is happening. It is a relatively new phenomenon and seems to be a victim of the last change VATSIM made to their servers. Any ideas would help please.