Re: How to debug
CP> This is the phenomen: Thin Client and Server work well, then -
CP> randomly - with a distance of a couple of days a single client
CP> looses its connection to the Xserver. It doesn't recognize this,
CP> so you can move the mouse cursor,
This is the expected behaviour. X11 connections are not keepalive, so
that a connection remains up even if there is an intermittent router
failure. (Think of remaining logged-in overnight, and coming back in
the morning after the router has been repaired.)
CP> Is it X11, KDE, Kernel or NIC?
Most probably neither X11 nor KDE.