That sounds like a defective pot. We see them about once in every 1200-1500 pots. Our QC process should have caught that, but sometimes the bad behavior is erratic and the unit works fine during testing. If you are willing, I will send you a couple of pots and you can replace the naughty one. Consult the kit assembly instructions to see how we assemble the unit into the cabinet, and follow it in reverse to take it apart. I will need your serial number (on the PCB, starts with ZD) to look up your order.
I’m very sorry for the trouble, but very glad you like/appreciate the design. That makes it all worth coming in to the Lab each morning!
Glen