I’ve been using 2 EV-1 pedals with my FX8 for a couple years now. They are both used as expression pedals so no audio is going through them. One is programmed as a volume control fulltime and the other for different effects depending on the preset. The problem is with the volume pedal. Recently, in the middle of a gig, the volume will not go silent when backed off all the way. There is a bit of guitar coming through when off. It did this in the middle of a gig. I took the cover off and physically rolled the pot back until it operated correctly. The next gig it did it again. When dialed all the way back, there is still some signal coming through. Any ideas what could be the issue?