Little Phatty SW19 button issue?

[TingxoGamchu]

I recently purchased a Little Phatty without USB and discovered that SW19 (OSC 2 LEVEL) is unresponsive. Despite attempting to clean the buttons, the issue persists. Even after removing the buttons from the PCB, the SW19 switch pad remains nonfunctional, although I can interact with other PCB switch pads. I've also reloaded different firmwares (StageSystem_v3_21_690 and 691) without success. All other parameters function properly. Are there any other troubleshooting steps I can take to restore echatrandom functionality to this button?