At this point you may need to have a service engineer to take a look at it.
Try turning on background suppression.
Enabling background suppression - https://www.support.xerox.com/en-us/article/en/x_alc80xx_en-O2243
Disabling background supressions - https://www.support.xerox.com/en-us/article/en/x_alc80xx_en-O13060
C8035/C8055- Scans come out with a solid yellow backround (Notably when copying double sided). Cleaned ribbon cable and cis scanner, as well replaced entire ADF. Still copies yellow.