Hi Vik,
I’m not sure why that would be happening but I do have one other suggestion to definitively narrow the problem down to the OSPi. Perhaps you’ve done this already, but do those voltage measurements stay the same with all of your valve wiring disconnected from the OSPi? If they do, it would completely eliminate the valves and wiring as the source of the problem. At that point you’ll have pretty much reached the extent of my ability to help but perhaps someone else will be able to chime in.
Mike