Help Random restarts after marshmallow, maybe

[theatremouse]

So I know that with Marshmallow a standard feature is that you can no longer unclock the device after a restart with a fingerprint; it asks for an alternate password instead, but otherwise is unlockable with fingerprint. Ignoring for the moment that I don't understand how this is an improvement since biometrics are more secure than passwords, I'm having a weird problem since the update. My phone seems to restart randomly, but not consistently, and not very frequently, but it's now frequent enough that I don't think it was entirely a fluke. Maybe once every two to three days it's been happening. The problem is that (don't tell me I'm stupid; I know) I don't actually know the alternate password. I store it in a password safe program on my home computer. So if I'm out and my phone does this random restart thing, I can't get back into it until I'm home, which is super annoying. I know the easy answer is: learn your own password; but part of the reason I went to fingerprint was so I wouldn't have to do that.

The other weird thing about it is, I don't actually think the device has restarted. I think it might just be randomly throwing the prompt as if it had. The reason I suspect this is the last time I observed the problem I had been out walking/jogging. So I periodically was checking the counter on my lockscreen to see how far I'd gone. And on these last two occasions, I clicked once to light the screen, glance quickly, then clicked again to turn it back off, and then just happened to click it a third time accidentally, and it was on the "your device was restarted" screen. Normally, when I intentionally restart it, it takes 30-45 seconds to do so. That much time had not passed between when I got the alternate password prompt and when I last looked at the screen. So now I'm wondering if it just for some unknown reason thinks it restarted and that's the real problem?

The other times it happened it had been in my pocket and I didn't think it likely I'd leaned on a button long enough to accidentally restart it; I have updates set to only download on wifi and was out of the house so I had wifi turned off at the time, so I don't think it restarted due to anything like that. So with this latest incident I now question if it actually restarted any of those times.

My question is this: does anyone know of any known issues like the above specifically related to the Marshmallow update? Does this sound like maybe some other type of problem with my phone? Is there any way I can check a log to see if/when it has been restarted? (or is that pointless because if the prompt threw the device thinks it restarted anyway and would state as much?)

I have cleared the cache. I do not run task killers or anything of that ilk. I am hoping to avoid solutions that involve factory reset. Just looking for info, if there is any to be had.

Model SM-G900V
CSC G900VVZW2DPF4

Thanks in advance.

 

[Avian960]

Same problem :C

 

[theatremouse]

An update, in case it helps you (or others). I have confirmed that at least with my device, it is not actually restarting. I was able to consistently reproduce the symptom by turning the screen on, off, then on again. Basically just push the button three times rapidly. Don't unlock it in between. That's when it happens and switches immediately to the "use alternate password" prompt. So I am guessing it's some sort of security feature (or bug) where doing that triggers the warning, and it's just that the wording of that warning is always the same and it doesn't matter if the device restarted or not. Probably because it's only intended to throw that prompt after a restart. But it happens when you do this too. So I've been trying to stop myself from the habit of checking my screen quite so frequently. I can always reproduce it if I push the button three times without pausing, but sometimes it happens even if there are a few seconds (up to 20) in between button presses.