Oh no! That is no good at all! I know this is probably a silly question but have you tried turning off the "Show when main screen is on" and then turning it back on again? Since this started after an update, it might be worth doing a quick cache wipe on the phone just to rule out any weird cache issues.
Hey there! This is such a bummer, I know a huge part of the appeal of the V20 is that second screen! Were you able to follow the suggestions that tmo_chris offered with any luck? I'll also add that it might not hurt to check your power saving settings and make sure that the second screen isn't set to turn off at a certain battery percentage. How is everything going?