If your battery connection came loose this would happen also. Presumably it became engaged again such that when you looked at your bag the green light was still on but you had to turn phantom power on again. Had this happen to me in my apt on a test drive within a day or two of buying it. 5 minutes later I mounted the thing inside a cage in backpack so that it could never get jostled again. It's been perfect ever since. I've been meaning to get some pictures of this as it pretty much elminates all the shitty things about the ergonomics of the box but haven't gotten around to it, yet.
Rusty