Hi,
some further update:
I have tried to enabled triple buffering in the xorg.conf-file (see How to enable triple buffering).
This results in the same frame being captured three times and skipping the two frames in between.
For me that is another indicator that there is an issue with the implementation of the graphics driver. Somehow it seems like a fixed buffer is being read and not the currently active one like it should be.
Can you please investigate this from your side?
Thanks in advance!