I'll answer my own thread once again

I have tried changing patch cable, no luck
I have tried a different port on the switch, no luck
I have tried a different switch, no luck.
I have tried a fixed IP-address, no luck
On the WiFi connection everything works according to specs'.
But WiFi and 4K movies is a bad combination.
So it looks like a RMA to me.
Does anybody have a link to information on how you make a RMA?