POST PICS
...or the most anyone can do is shoot in the dark and suggest you reflow the solder connections for that pot, C17, FV-1 pin 2, and TL072 pin 7 — although the latter should be fine as you say everything else is working properly.
If you want to fix your car you have to show the mechanic the car, you can't just describe the car's problem over the phone;
Post some pics of your build and somebody will hopefully be able to help you.