I noticed these, just a week with a brand new g2 behind: if I DON'T have the voice helper thingy listening at lock screen, the phone will randomly shut down. It started doing this 10 times a day when I turned it off (because it doesn't work with just speech anyway, just says no network and thus it's of no use), and
I was ready send the phone back, when I realized if I had lock screen voice command back on it worked...and, not one shutdown since.
Also, the moment I turned on screen lock security, the phone started losing network when screen was off and ask for PIN code many times a day. Removed the screen lock and made it just a swipe, and no issues since.
Probably if I had not let it install any updates it would work fully.