I can relate to your problems with the AFCI. I had an AFCI that was installed in new construction that would trip as soon as any load was applied on the circuit. I immediately started thinking through the possibilities of Hot to neutral arcing or even neutral to ground connection, but thankfully before I started taking everything apart, I checked the panel and found that I had connected the wrong neutral wire to the AFCI breaker. Thus whenever a load was applied, the breaker was sensing a ground fault since there was no equal current returning on the neutral wire. Needless to say, I was humbled and was reminded that sometimes it is the simple things.
P.S. Please forgive me for saying neutral instead of ungrounded conductor