Is it your monitor screen that has the grid pattern or the actual print? I have the f135+ (since 2013 or earlier) and have never noticed this type of scan problem. I know the 235 uses a different light source than the 135 or 335 but that wouldn't cause the grid problem. You can run a scan calibration tool which is in the software (tlx or psi). There is also a FB group for pakons that has been around a very long time, if you can't resolve the issue, you could ask there.