stupid thought here
does the 3.1 have external switch for power or the one located on the ESC ?
if its the external switch you have to hold down calibation button as you switch on to get into calibration mode
if its the one located on the esc itself i think you have to hold "power" button in as you plug in battery to access calibration mode
im not 100% sure and you may already know or be doing this
just another avenue to try if you hadnt thought about it or done it
best wishes Dave