I don't think I've had this happen to my iPhone 7+ yet. It was my 6+ that had originally had me start this thread. However, it hasn't been very cold since I've gotten my 7+. I always seem to have these kinds of issues during cold streaks. Winter hasn't really hit here yet this year.
When you check your battery usage, I would think it would show camera usage, not lock screen usage though. Maybe I'm wrong. Mine clearly showed lock screen using all my power.