Erratic behaviour in display rendering
 

Hi
I have an AOC international 27" 4K 60Hz display and a Dell XPS 13 9380 running
debian buster.
I can't get the AOC display to work properly.
1. Despite being a 60Hz display, the monitor manager sees it first as 30Hz.
2. The monitor manager keeps asking to configure the device but it only shows
a black screen.
Could it be a BIOS configuration of the thunderbolt?
Could it be that the software cannot use both monitors at same resolution
but different frequency?
Any suggestions?
I use the debian port of the driver from git hub.