Saw this once, I think, right at the start. Give the car a drive for a while to get the 12v charged and it'll go away. I don't think mine has been back since the early days, when presumably the car had been sat around on a boat and then the dealers for a few days.
In a year or two if it comes back then it might be sign that the 12v is starting to fail; it seems they put pretty cheap 12v batteries in the Niro, so worth keeping an eye on this status.
I got mine last Friday and got exactly the same result when I (finally) hooked up to UVO. As @DragonQ said here, I sat in the car for half an hour (actually, my wife did the sitting) with the car in Utility Mode, and the UVO warning went away. I never found out if it was a false warning; didn't have to after the U Mode episode.
If the 12volt battery gets too low then it can prevent the car starting at all. I suspect that the 12volt battery may get particularly low on the voyage to this country. I put mine on a smart 12volt charger and it has been fine as far as I can tell most of the time since. An alternative is to put the car into utility mode for 2 or 3 hours to help the battery recover.