Yep, same here for me watching Sky Max live on my Youview box and NOW 4K box.
Where Sky Showcase live (currently watching Will & Grace in the background is streaming fine).
Hopefully it's teething problems with the new Sky Max service (haven't tried any Catchup or on Demand content yet from the Sky Max library) to see if the error is relating to the live stream only.
Looks like it's only effecting Sky Max live at the moment with the error message shown on your screen shots.
Where i just tried a TV show on Sky Max catchup and it was running fine for the 10 minutes that i tested it.
Hopefully the bug will be ironed out shortly by NOW.