There are several solutions. A. Speed vs Quality. You can change the speed setting adjusting these settings. There is an inverse relationship between speed and quality. The faster speed the scanner goes, the worst the quality.
Some software does a high speed, low quality preview, and low speed, high quality scan.
The problem is that there is not an exact match between the preview and final scans making some color correction adjustments done to the preview scan erroneous. You can turn the high speed to do the preview and click on high quality to do the scan if you choose to. B. Preview Resolution. The higher you set the preview resolution in the preferences the slower the preview scan will be. The lower you set preview resolution the greater the chance the fat bits look.