Recently I upgraded from Win8 to Win10. I used to run Cygwin/X with a
window manager (dwm) without any problems.
After the upgrade this did not work properly anymore. I can still run
the X server and dwm starts as expected. However the window does not
seem to be refreshing/ repainting correctly. Nothing appears when I
start an xterm and type something. When I move the mouse around and
click a bit, parts of the screen update and I see the xterm and the
commands I typed.
I tried a different window manger and no window manager, but just an
xterm, all with the same behavior.
When I run xterm in multiwindow mode it works as expected.
When I run in fullscreen mode (single window) everything also works as expected.
I tried the Cygwin 64 bit version, it works in the same way.

Any ideas what could cause this?

Regards,
Joris