There are a few reasons why before and after scan does not work correctly. One reason is that the app may be trying to compare the old and new scan data, but the old scan data is not compatible with the new app. Another reason is that the app may be trying to compare the scan results, but the old scan results are not compatible with the new app. Finally, the app may be trying to compare the scan results, but the old scan results are not compatible with the new app because the app is not compatible with the old scan data.