<opinion alert>
I have heard lots of AFCI stories and my thought is these problems are in that huge cludge of white wires under a wirenut in a ceiling box. You know the one I mean. Back in the pre-AFCI days if the neutral had some incidental contact with the box (hickey or whatever) because of rough handling <pinched> or simply a little too much copper sticking out, there was a technical violation but the light stayed on. Now the AFCI trips. A fan shaking the box will make this an intermittant failure and make it easier to "prove" AFCIs and fans don't get along.
<opinion off>
