The ARC Fault Breaker of one of my bedrooms turns off. I cannot turn it on now. What could be the cause? By the way, I have turned off all the switches. What should I do from this point on?

A related interesting question is why the night light that I plugged into one outlet in the bedroom is still on, isn't the outlet subject to the protection?

Remove wires from the load side of the Arc Fault breaker(black and white), try to reset.