Passenger window

Something that normally fixes/confirms it is, with the door trim on and door closed, give the door a stern thump with your fist a few times while working the switch. If it works then, should work for a while but does need replacing at some point

Agreed. My wife found a comment in a forum to thump the door panel just above the speaker. For some reason you have to do this while the car is running. Weird but it worked, and has worked multiple times over 2 years.