Vero 4k+ stuttering Video

Hi,
i switched from a Raspberry Pi3 OSMC/Kodi to the new Vero 4K+.
I have tried different movies to play from the usb HD (720/1080) i used before with my Raspberry without any problems.
Can somebody explain what can cause stuttering video replay on the Ver 4k+ ?

Regards
Anton

Do you have adjust refresh rate set to on/off or always?
Otherwise Mediainfo of the files would help