When using the OX9 with an Expression Pedal, the right switch/button can be used as a Hot-Switch (e.g. for instantaneous octave-bends with the PitchFlex), but as soon as I use it, it decalibrates the formerly calibrated Expression pedal which then only has a limited range.
Is there any way to resolve this?
There's a system setting to turn expression pedal calibration on or off. You should turn it on to calibrate your expression pedal and then turn it off to lock out any further changes. Incidentally, toggling this setting causes it to forget the previous calibration, which can come in handy.
To get to this setting in H9 Control, press the Pedal button in the bottom menubar, go to General Settings, and then to Pedal Calibration Disabled.