nice work, just built a 20m mini here.
the 7 level on BPF peaking means little - it changes as you adjust volume control. as long as you get a pronounced peak, all is well.
the other nulling calibration is more important, and sounds like that went well. note it takes several iterations and each menu setting and knob to get it optimized.
20m propagation has not been great recently. i managed a few WAE contacts this past weekend, but not much since. so hang in there.
5 volts on coax center pin has me spooked - check it again with no antenna attached. I confess I have not looked into that, check the schematic and see who else comments. there should be a blocking cap that isolates the center pin from the circuitry - and with EFHW likely introducing a DC short - I am saying how can this be if the blocking cap is shorted - check it again.
73 Curt wb8yyy
fellow QCX traveller