You should have the GUI on 1080p already. You don’t want to run the GUI at 4K all the time, just enable Adjust Refresh Rate and it will change to 4K when you play 4K content.
(Maybe a sticky on this would be good, because it seems that I’ve been missing information, despite reading what I consider to be fairly diligently!)
I preferred to keep the GUI at 4K because my projector takes quite a bit longer to switch resolution than refresh (around 11 seconds). But obviously I won’t do that if necessary.
If (for whatever reason), I’m supposed to keep the Vero at 1080p, then there’s “no issue.” 1080p plays back at REC.709, and 4K plays back at 10bit/BT2020.
FYI, I thought you’d be interested to know (now that this bug has occurred twice), that when I switch from 1080p to 2160p in the GUI, when playing a movie the picture completely dropped, instantly. As in, signal gone. A reboot of the Vero sorted it, but it’s happened a couple of times after setting back the GUI to 2160p from 1080p.
In any case, I’ll leave the GUI at 1080p from hereon out, and leave the forced 10bit for my JVC (assuming the actual toggle never works for me in the future).