bad app? that's often the cause of freezes, lag or random reboots, or a faulty SD card or card slot.
The only thing i've noticed with my G3 is a slight lag before the KnockON turns the screen on. enough to wonder if it actually took your taps, but i think that's because it's also waiting for my KnockCode as well, so it takes three seconds, then the notification light turns on, another second later the screen wakes up.