possible cause and solution of jittering of pots..

Testing/Troubleshooting
1

I read recentlly that leaving flux residue on boards can cause problems in analogue circuits due to leakage (flux acts as a resistor)

I’m getting a can of PCB cleaner!!

2

Forget that. As long as we are not talking about mV (e.G. in sensor technics), the resistance of the flux is muuuuch more than enough.