Volca Keys - No Sound from specific keys

[georgehurleyssockstick]

Hello,

I recently got a secondhand Volca Keys. After a few weeks of using it with no problem, the high F and high C# have stopped producing any sound. It sometimes seems that other keys are not as responsive to touch as when I first got the synth. I've tried replacing the batteries and performed the firmware upgrade, didn't resolve the problem. Anyone else experience this issue? Thanks.