I posted this in the other thread related to this on my 2 808s... make sure you check the screw on the scanner drive gear on the back right of the machine accessible by removing the top right cover. there is a screw that secures the gear to the metal drive shaft. This screw comes loose and is too short from factory. Replace this screw with a longer and it resolved our scanning issues with identical symptoms.

KM will be releasing a bulletin on this directly.