I've also had the soundbar for about 6 months.
I often watch TV quietly when someone in the house is asleep, but I have never noticed the sub switching off and on.

I've been using the soundbar for a few months now and haven't experienced anything like this. It works perfectly so far, as it should.

I've only had it in operation for about a week, but so far everything is running absolutely great from my point of view.
However, I don't know if I would notice if the subwoofer switched off at low volume. It only really comes into its own when you're on the move with a bit of "boom".
I, for one, am thrilled with the price-performance ratio of this soundbar. And the Clear Voice button is a great function that improves the well-known problem of poorly audible voices in surround a good step, if you have to watch a little quieter in the evening.