Something is no longer connected.
You will have to pull it and examine all wiring but start with just the In and Out wiring that leads to the In and Out jacks.
Reflow and make sure you have a solid connection to a good solder joint. Check both onboard and off board wiring.
Be sure to also check for any shorts such as what happens when both cables are plugged in and see what is mechanically happening inside (for example make sure the tip of the guitar jack is not bumping up against IC pins). While you are at triple check your cables.