I am experiencing a similar issue.
I recently got a second hand VPM-1 that was the ready to install version.
When I rock back the pedal to the silent position slowly, it get a slightly distorted sound in the last 5% or so of volume decrease.
When I rock the pedal back quickly to go silent before then swelling up another note, it takes about a second for the signal to truly go silent even though the pedal is all the way back. I am recording my guitar straight into my interface with no extra gain. I’m also using headphones so I can hear this clearly. When I use my analog volume pedal this doesn’t happen of course and it clearly goes silent immediately.
I have done the stereo calibration as well as tried several taper calibrations ensuring that the “0” point is not all the way back. Any ideas?
I love this mod for it’s low noise and for the perfect taper for slide playing but the lack of true immediate silence doesn’t work for what I’m doing.