Might I suggest moving the pitch bend wheel vigorously from minimum to maximum several times ? Especially if you don't use it often, some slight oxidation might have happened inside the potentiometer. Giving it a good "workout" might help clear the issue by friction.
And of course, recalibrate it after doing so.
If that doesn't fix the issue, then I would suggest, like shiihs said, to contact Sequential Support about it, via e-mail or phone.