I have the same problem. Based on the behaviour it seems like the phone is closing or suspending Nova when it is in the background. I've tried adding Nova/Nova Prime to the never sleep list, but this doesn't make any difference. The phone should recognize the active launcher as a special class of app and only close it or put it to sleep under extreme memory pressure, which makes no sense on a phone with 6GB of RAM. As other have said the screen flashes if I touch it within 1-2 seconds of returning to home. Although I've seen a few times when this hasn't happened, but there isn't a pattern. It seems Nova is put into a sleep state, with the UI context being cleared and I think the flash is showing Nova resume/refresh. I've had my phone reset back to the default launcher randomly when unlocking about 3 times in the last month and I have to add Nova again via the settings menu. When swiping up to home sometimes it ignores the gesture but if I wait it works again, which leads me to believe that Nova is being closed.
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