Every now and then, a bathroom GFCI (nothing plugged in) randomly trips, and also sometimes (<5% of the time) when I turn on the light switch in that bathroom. The bathroom has a GFCI in one box, and two switches (in one box) for light and exhaust fan (not above shower). I assume the light and exhaust fan are not downstream from the GFCI since they remain on when the GFCI has tripped. I also assume all components are around 17 years old.
That GFCI seems to have a downstream connection to another GFCI in another bathroom. I assume that second GFCI just needs to be a regular receptacle, but that is another question :). A GFCI tester indicates correct wiring for both GFCIs.