If you're still experiencing the issues described in this thread, here's something to try. The next time it happens go ahead and turn the climate control system back on, but leave the instrument cluster alone and at default (with the top down view of the vehicle). Don't change it, don't scroll through the settings, don't touch it at all.
I was having this issue occur randomly and fairly frequently, but it seemed to occur most often when the fuel tank was >50% full and always the next day after filling up.
The last time it happened the fuel level was at ~80%. Since leaving the instrument cluster at default after the last reset it hasn't happened since, and I am on my second fill up with the tank around ~50% at the moment. Btw, my gauges are configured for the 3D cube.
Could be a coincidence, but that's been my experience so far. At least the average MPG indicator is useful now if nothing else.
I am waiting for Hyundai to come out with a verified fix (TSB) before I take the car in for this issue because I can't be without it while the dealer tries to figure it out. I did mention the problem while scheduling an change in May, they looked into it, and came back with there's no TSB or FW update available. It was then suggested that I schedule an appointment to drop the car off and have it diagnosed to the tune of $175; refundable if it turned out to be a warranty issue. I've no confidence in the dealer, so I'll wait for Hyundai to acknowledge and fix the problem first.