This problem appeared yesterday morning with seemingly no cause. I went to bed with the phone working just fine, and when I woke up, it was locking itself. I have been working on solutions for hours now, resetting the cache, trying to disable the lock screen, making sure no buttons are stuck on a case, etcetera, all to no avail. I'm tempted to give up and factory reset the thing, as no one seems to have this problem, but there are files and photos I would rather get off of the phone. Files don't appear unless I have it unlocked, though, so the problem goes full circle. At this point, I'm open to suggestions.
Do note, I was playing around with a feature called "Screen saver" in the previous weekend, and the previous night my phone crashed while using Google Maps and VLC Media Player at the same time, so maybe there's a memory problem a reset can't fix or I just made some horrible combination that bricked this thing.
Solved! Go to Solution.
In the seconds I had before it locked itself, I backed up my photos to google drive and selected "share" to text my contacts file to a friend. Then I reset. Yeah, I have no idea what was causing it to lock itself, but a reset definitely stopped it.