I may have misunderstood your previous post. I thought you said that you had a batch of these coming and you were going to open them up and repair the grounds and possibly install new chassis grounds to board before you distributed them.
I asked you to take a few pics of the repair process you employed when you did so to help others and post them with your findings as with a large batch of units you will probably be the best person to find the most efficient repeatable process and are obviously skilled in what you are doing.
Should I have tried to volunteer you in that manner without asking politely - no. For that I am sorry. If you choose not to do so fair enough.
We all agree the OP has probably got a poor connection issue and many of us would choose to diagnose it ourselves with an ohm meter on each connection starting with the 510 to top plate right on through each connection but the best advise I would give him is to return his warranted unit to fasttech for manufacturers replacement based on his reported skill level.
I have 2 Waideas & a Kangxin not an SXK so I have only been speculating.
@Tpat591 no worries I must have read your post wrong
I will test all
Should any be faulty I will be doing as you clearly stated and pulling it apart & checking all the wiring and resistance of the +/- circuit
Will make a point of taking some pictures of what I do