From the HF signals schematic and wire-up diagram (original V3 sourced in ~Feb/March 2018), it doesn't look like the designer anticipated that the Mic/PTT plug would be plugged-in after uBITX power-up.
I think this is where Raj is going when he suggests swapping PTT and Mic wires (on both the uBITX and your mic)
The original supplied V3 wire-up has:
Tip = "Mic" = 4.7K ohm resistor to TX (12V when in TX mode)
Ring = PTT = internal Nano pull-up to 5V
Sleeve = GND
When you plug in a TRS plug to the jack supplied in the kit, the Sleeve to Ring (jack side) can easily short if it is off on angle.
The internal springs in the jack help get the plug off angle (at least on mine)
A short between PTT and GND puts the uBITX in TX mode.
As you continue to push in the plug, you short Tip to Ring on the jack. (You can see this through the clear plastic window on the jack)
For a brief moment if your uBITX went into TX mode, a second operating condition fault scenario: 4.7K Ohm pull-up to 12V on the Nano.
Now you are depending on the ESD protection diodes internally to the Nano to protect from Electrical Over Stress.
Swapping Mic and PTT positions would seem to be more robust (I have not fully vetted this solution.)
You would still have the above Tip to Ring fault mode if you accidentally unplugged the while the uBITX was in TX mode.
(so not 100% robust, but that is much less likely to happen often enough to be of much concern, and if the Nano goes 'bad'; you have a clue)