Unexplained amperage spikes
20.6 A would be a major overload for the UPS. If the UPS isn't reporting anything unusual -- and circuit breakers aren't tripping -- you have to entertain the notion that the reports you're getting from the WattBox are simply wrong.

20 A is almost 2500 W, so yes, something would be getting hot in that amount of time! Also, I'm assuming that the whole setup is plugged into a wall outlet that's only rated at 15A.