Huanyang spindle speed control issues with output control board and 0-10v

Posting this mostly for the benefit of anyone that had the same issue, who happens to be searching for a solution.

I am running 2.2kv huanyang vfd with mk3/4 planet-cnc controller and output control board. Its wired for 2 relay 0-10v spindle speed control via TNGv2 on a Rasberry Pi. Settings were all correct per how-tos on planet-cnc site

I was able to control the speed, but not very reliably and not to the full speed range of 8-24k rpm. I had the set the s value to a speed that would "trick" it into running close to the speed I wanted. For example, S5000 gave me 16k at 100%, which I could dial down to maybe 13k.
What I found was that the output of the output board would only go down to about 4v. Disconnected the wires from the vfd and measured the vtage again. Now it was putting out exactly the right voltage throughout the 0-100% range. S24 = 10v at 100%, and 8k ( the minimum ) at 0%.
I run shielded wire that is grounded on everything on this machine - including the wires that ran to the 0-10v signal. I cut the ground wire, and the problem was gone. Works beautifully.
All I and think of is that there is some kind of loop/short into the ground and it was inducing a current in that line? The weird thing is that I had no other running issues with it. I'll have to see if I can figure out where the leak is coming from and how much...

Anyway, if you're having controller weirdness, and you're not an electronics expert, check your shielded and grounded connections. Hope this helps someone. I struggled with it for months.

Drew M