I cannot trace the wiring with that photo alone.
If it were me the first thing I would do is re-flow all solder joints on and off board. (about 15 minutes)
Then I would re-check the Audio path wiring. You can also do this by doing a continuity check with your DMM and making sure every single point is covered with Ground and Audio wiring. From main board to jacks from main board to foot-switch.

I would also trim the transistors and make sure they have a good mechanical connection.
If all of that fails report transistor voltages.
That is what I do for ever troubleshoot and yes we all have them from time to time.
I hope that helps.