The schematic generator cannot instance one channel sheet N times, so each channel gets copied into its own file, and the copies drift. On a hi-fi receiver, the left and right amps pair only 25 of 44 parts, 8 of those pairs have different footprints, and 17 plus 19 parts have no counterpart. The board import also drops each part's sheet path, so KiCad's own repeat-layout tool cannot match them either.