Your keystation might need a surgery. I know I had to perform surgery on my oxygen 61. In my case it was sending a quarter tone down. Opened it up, recalibrated the wheel, still works.
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I agree. It’s still not right… I went to a track and the enture synth down a full note. and no pitch bend data.
I have a Novation 25sl and also run into this issue from time to time. A synth going out of tune all of sudden. I fix this by nudging the pitch bend wheel and that resets it back to normal. I guess it’s perhaps time to buy a new midi controller 
But i still like my little novation. Another thing that bugs me is that i can’t get it working with Midi Remote.