First try to update the machine software.
Second, disconnect and reconnect the SBC board and everything on it (that one with network port on it, it have three thumb screws and a handle).
Gray background on 1st side, B&W. Yellow background 1st side when Color onlt thru ADF. Have cleaned glass and ran copy calibration to intermittently fix this. Returns after about 2-3 weeks. Anything else that can be done.