I too have this problem and I have the latest firmware. I've also reflashed it to previous firmware versions but is still the same!
it also happens if I map the fader in 3rd party software. plus if I remap it to another functionality within rekordbox the centre still has a bad 'dead zone of about 10mm.
both left and right sides work true.... just the centre position has major twitches!
I can't use the crossfader until it's fixed. to me the audio is noticeable in abrupt transition movement.