My upstairs hallway lights are controlled by a four-way switch circuit. There are three switches to control two dome lights. One switch at the bottom of the stairs, one at the top and one at the end of the hallway.
When we moved in a year ago any switch would turn the lights on or off without issue. Recently the switches don't seem to work. Then randomly the lights will turn on. One time my wife noted that when she flipped a switch the lights flickered but remained off. I think it is a loose connection of a bad switch, but I am not sure how I diagnose the root of the problem.