Most breakers are overrated. For instance I was putting the clamp meter to our panel to get actual, real life information on amp draw of all our devices when they run full tilt. Our Chili is on a 30a breaker but, with the power at max and all zones on, that clamp meter was reading out a steady 35a draw or more. The breaker did not trip, never has even in heavy production. Could be the tolerance of the clamp meter but it's a good one, not a cheapie and nevertheless, that circuit is getting redone and #8 with a 40a plug/recept and breaker setup.
So your case sounds like a faulty breaker or possibly some kind of weirdness in the machine on the circuit. It's unlikely the mfg listed the fla incorrectly. You should absolutely not be using a 40a breaker on a device with an fla of 20. 30a breaker should be more than adequate there.
*none of the above is offered as actual electrical advice. I, or anyone posting on the internet could, in fact, be a total dumb ass. I am not an electrician, be sure to consult yours.
