I will be following this thread for sure, curiosity is killing me.
I cant bad mouth AHP to bad because I will take some of the blame for my mistake but I think safe guards should have been built in, this was my experience.
I generally favor stick welding and I loved the way the AHP alpha tig ran 7018's, the smoothest I have used. I decided I would play with the tig function and got everything set up BUT I forgot to toggle back to tig. from that point on the solenoid never functioned correctly again. it would open for about a second and close right back up, sometimes it would open a second time for another second or so and close again. like the OP I went through everything I could think of and couldn't solve the problem so I returned it and bought a square wave 200.
I truly liked the AHP, it runs stick significantly better than the SQ Wave in my opinion but I didn't feel comfortable with a machine that was that delicate. as I said I will admit my mistake but forgetting to change modes shouldn't take a machine out.
in defense of AHP I sent an email ( not about this event just a general inquiry ) and 10 minutes later my phone rang and it was the owner of the company, the same thing happened when I emailed EverLast, I am still amazed by that.
good luck and I hope all goes well for you, I cant say I wouldn't try AHP again for an inverter arc welder.