Kevin, thanks for confirming!
I have to admit that in my case it was the mini HDMI to HMDI cable causing problems. I sometimes had video out, and sometimes not, with no visible pattern. I tried an Amazon Basics mini HDMI to HDMI, et voila. Always video output through mini HDMI. I'm not sure if there are any differences between the two cables I tried, but now NUC works as planned. I'm very happy with this NUC...
Again, thanks for your help, perhaps changing cables will help others too.
Chris