One of my windows 10 pc's always lags a bit when using microsoft RDP to remote into it, with no obvious reason as it is on the lan and a fast connection.  Tried all the obvious things to fix. 

 

After more extensive googling, just discovered others have the exact same issue...

 

https://superuser.com/questions/1137697/remote-desktop-develops-mouse-keyboard-lag-after-some-duration

 

So, the rdp lags when the remote machines attached monitor enters 'sleep' mode.     I have confirmed this, and the fix works. 

 

The remote machine is gigabyte z370 mobo with intel integrated graphics.    

 

I have another almost identical machine, but with a gtx1070 graphics card and that does not suffer the issue. I'm guessing it must be something to do with the intel integrated graphics. Updating the driver does not help. 

 

Anyway, this most frustrating and unusual problem is solved.