I have the latest update on my Niro PHEV with GEN5W screen and this is still a problem.
Yesterday I made a journey to a car park set away from the side of the road up in the mountains. The road leading to the carpark is a major enough road, an R road in Ireland equivalent to a B road in the UK, so you'd assume it'd be present in the speed limit database.
Anyway, driving there, the display showed the correct limit of 80km/h right up to the point where I turned into the car park, and kept showing 80km/h when I parked, presumably because I was actually only a few metres away from the road, but some distance before that I had passed an 80km/h sign, so no idea if the displayed limit was as a result of that or what.
Spent about 6 hours there, and driving out of the car park to head home, the display immediately showed '---' and kept showing that all the way to the same speed limit sign I'd passed on the way there, except the reverse side of it, showing 50km/h and everything was fine from there all the way home.