Maybe help for some others…
When I play 4K content all good, but when I play one more 4K content after 4K content, the movie just seen on 1/4 screen.
I have clean installed for another sd card, and then another usb3 pen. Issue still remain.
Workaround just when I set to gui resoluition to 3840x2160p 60Hz. But that nogo for me. Currently after playing one 4K content, I play one HD content for 3-4 sec, then all good again when the GUI 1920x1080x60. I can live with that… 