Glad to have found a place to ask questions and post findings on this hateful situation.
Note 2 SGH-i317M (Rogers, Canada) for about 2 years without a single issue until a couple of months ago when random shutdowns started.
I've uninstalled all apps. I've soft-factory reset (have *not* hard reset it yet). I have even rooted it which oddly has made it worse. Does not turn off if something is running. IE: if it is just sitting it is likely to turn off but if I'm talking on the phone, watching Crave or Netflix, listening to music, etc it NEVER turns off. It's like a standby state that engages and it drops into a coma...
Things I've noticed:
1) happens at home almost exclusively between 4pm and 4am
1a) happens more often with wifi on
2) happened only a few times outside my home
3) almost always when the phone comes back on there are apps to be updated that didn't need to be updated earlier in the day
4) since rooting, it shuts off 100% reliably between midnight and 4am (when I get up to pee and notice it's off - lol)
4a) overnight shutdows happen plugged in or not
4b) if plugged in, the battery is ALWAYS at 95 or 96% charge after it comes back on
4c) if not plugged in, the battery drops from 100% to 45 or 46% between 12am and 4-5am. During the day the battery goes from 100% at 6:30am to anywhere from 50 to 65% depending on use during the day when I get home at 3:30 so the 55% drop in 4 hours overnight is crazy... During the day it lasts all day. Overnight it doesn't. No clue what it's trying to do overnight.
I've tried safe mode early on in this process and it didn't help. I will try it again this weekend to see if it behaves differently now that the other things (soft factory reset, rooting, etc) have been tried.
Tonight specifically I will experiment with airplane mode to see if that does anything differently. If it does, I think I will start to block apps/services with the Avast firewall and see if I can find a suspect.
This has been quite the ride... the phone was 100% reliable for the better part of 2 years and now I can't trust it.
Any and all thoughts appreciated.