Hi,
Does the Keylab controller have a calibration function for the wheels?
Does the Pitch wheel output a modulation, when it happens? Have you checked using a midi monitor?
I can't be sure. But to me it sounds like the Pitchwheel output data. And if there is'nt a calibration option for to regulate this, them it perhaps can be dirt or an error with the wheel. If it's not dirt, then you perhaps need a new Pitchwheel or a Pitchwheel repair, if you can get that fixed. If it's dirt, it perhaps can be fixed with a cleaning that follow the guideline for generel cleaning in the manual.
If the keyboard is'nt too old, then perhaps this can be fixed under guarantee.
Please keep in mind, that this forum is'nt Arturia support.