You can test the speed sensor output to the Healtech with a voltmeter. It is just a square wave signal of about 2~3 volts.
Wish you were close by, I would try to help you sort it all out with enough documentation to convince Healtech the unit is defective, if it is.
I haven't installed one of these myself, perhaps there is a wire continuity problem from the sensor connection to the unit?
I can perform that test and I very much appreciate the offer / condolences
Honestly, I was put off by how all this has transpired and have not researched any further. I will jump back on it this week and update the thread with what I find