I had a pink screen again this evening. Switching to HDMI 3 and HDMI 4 I got a green screen, as I did when I plugged it back in to HDMI 2.
A power restart of the VTV (Gen 1 box) fixed it.
To be blunt, I should not even need to be trying this ... the box and firmware provided to me should be capable of driving a modern Smart TV from any HDMI port without such problems. In my view this is a defective system. If the updated firmware doesn't fix it, I would expect to be provided with a Gen 2 box in the hope that would work properly.