It's possible the pickup selector switch has a dirty contact for the front-pickup when in the middle position. I have an old Ibanez that does the same thing sometimes when I switch to the neck pickup.
I haven't seen what type of switch Epiphone guitars use, but my Les Pauls had an open-back switch, so it was possible to take off the switch cover and carefully squirt some contact cleaner on the contacts.
Contact cleaner can be found at electronic and hardware stores. It's a very light lubricant that helps to flush out dirt or debris that can affect potentiometers and switches. It is NOT the stuff you'd use to clean your contacts that go in your eyes.