Samsung Patent application US20160173800 "Image sensor for performing coupling-free readout, and device having the same" by Kyoung Min Koh, Ju Ha Kim, and Jae Cheol Yun talks about the coupling between the column-parallel ADCs:
"A coupling effect is generated between adjacent analog-to-digital converters by parasitic capacitance that is present between the adjacent analog-to-digital converters. In particular, the coupling effect which is increased as a difference between pixels signals becomes large increases non-linearity of each of analog-to-digital converters. The non-linearity is one of sources of errors of an analog-to-digital converter."
Samsung team proposes to change the pixel readout order so that the pixels with similar values read simultaneously: