Well, the problem fixed itself. I went back out to the Niro at the end of my work day, and the left screen was working normally again. No explanation for it. It might be a loose connection, but the fact that it only happened when the car was turned on or off leads me to believe it's more software-related than hardware. So far it hasn't gone out again. Very strange. I'll update if it happens again, but for now it's back to normal.
I hope for your sake it's not what happened to us. I started our Niro EX one night in February and this exact same area had a problem but very different from yours, gas meter was completely empty of the little boxes, miles to empty flashing, gas tank icon flashing etc etc etc......long story short, a little critter/rodent got on top of our gas tank and chewed the wires to the fuel pump, it's part of the main wiring harness, NOT under warranty, entire wiring harness had to be replaced, which involves removing ALL seats, floors, carpet, center console, dash, and trunk,,,,,,,,,,, $2,200.00. Seems that most all manufacturers starting around 2008 (and NOT just hybrids!) in an effort to both be more environmentally conscious AND reduce cost, started replacing traditional plastic and rubber coated with SOY and CORN covered wires!!! Food buffet for rodents!!!! Google search "Soy Wire Lawsuit" and you'll see that several class action lawsuits have been attempted but none successful yet............. one poor guy had his new Honda SI for a few months before $14,000.00 in damage was done under the hood by rodents............... fortunately for us our insurance covered ALL but the $50 deductible...............many dont add "comprehensive" coverage on their insurance and end up paying thousands in repairs............... this will end up being far worse than the "air bag" recall as the job to replace a wiring harness alone was several days work............ using soy/corn coated wires was a good well intentioned idea gone very very bad. Now many people with strange little problems, many even intermittent like yours, are finding wiring damage from rodents,,,,,,,,,, they can smell that "food" from outside the car and they pursue it........... big problem