Amp tripping circuit breaker.

If it happens with the amp plugged in and turned off there is a statistical certainty its not the amp

so far that hasn’t happened, since I’ve kept a log

And yet this did not trip the breaker. This is what we call a "clue".

Are you implying that the amp tripping is an independent issue from the breaker?  maybe I’m not following.

I am a certified electrician. And I believe part of the problem is the AFCI breaker since it is known to be a common problem with them and GFCI types. Also confirm if you are using a 29 amp breaker with at least 12 awg. Wire otherwise you are overloading the circuit with your rack setup. Just because the breaker says 20 doesn't mean the romex in the wall is suitable for such a load. 

I would find out what the amperage is under load with. Conventional amprobe  at the panel. And if you are exceeding 16 amps then you are using more than the breaker can handle for long term use. 

I would recommend a dedicated circuit with at least 12awg  10 would be best. and have the electrician or yourself balance the loads between your 2 legs at the panel. By moving some wires around to come up with the most balanced load on your hot legs. 

I have seen tripping on breakers from loose connections both in j boxes and receptacles. And in some cases the wires can overheat and melt before the breakers actually trip.

Hope this helps.
 

I meant 20 amp not 29 amp breaker.

Yes it’s 20 amp wiring.