another remark:
I have closed putty, closed Thin VNC server and restarted win10- kindle DXG with 3.3 OS remained connected to the PC.
After boot it occured - that my wifi connected a bit later, but in the meantime without lanuching putty and manually typing in script lines - only with ThinVNC server running - my kindle started working as 2nd display right away.
So maybe there are some connections between apps that have not been fully tested / recognized.