I've posted this on an android forum, and found others having same problem. After the latest software update in Aug, the Auto Restart feature stopped working on both my wife's phone and mine, we have AT&T (SM-N975U).I have cleared the cache in the boot rom on both phones, and it still don't work. I've tested it in safe mode, even factory reset phone. It seems like the phones try to restart, but something is preventing it from doing so. The screen turns on at the time it's usually turns off.. Ex: set to restart at 4:00am. Phone tried at 4:40am. This was the usual time it did it before update. Basically, It looked like it restarted, I had to put in my PIN when I woke up and it even said, "Enter Password after a restart" HOWEVER, If I go and look at the "up time" in settings, it showed 14 hours and 31 minutes. Also, it didn't do the "Restarting" across the screen that I usually get when I restart.
Also, Do Not Disturb mode has a bug. It turns on automatically, but if you turn it off after its scheduled run, then manually turn it back on, it won't shut off. (eg: Auto run=9pm-7am. But f I turn it off for any reason during that time, then manually back on, it stays on till I turn it off again). This never did it before.
Galaxy S10 user here with the same auto restart problem. The screen comes and the device appears to restart EXCEPT for the large S10 logo with the little green Android robot. This began after the October 6th One UI 2.5 update. The subsequent security update around October 21st did not fix the problem. BTW, I did clear the cache partition to no avail. After seeing so many threads and posts about others with the same issue, I left it at that, as it's clearly a problem with the update itself. Please resolve these issues, programmers.