Vortex Sound Research

Hi! My Sub Phatty is detuning while playing, you can hear pitch descending and ascending between 0 and a semitone down. And when I touch the Fine Tune a little bit it jumps back to 0. I tried to let it warm up, I restored factory presets, I tried to automatically calibrate. What else can I do? SEE VIDEO! Sub Phatty tuning problem