How to increase the maximum file size to scan
By default the Website File Changes Monitor plugin for WordPress does not scan files for changes that are larger than 5MB. If it identifies a file bigger than 5MB during a WordPress file changes scan it notifies about it so you know it was not scanned.
If you do not want the plugin to scan such files exclude the files from the scan. Otherwise, for the plugin to scan these files for changes increase the file size scan limit from the plugin settings. Specify the new size in the setting File Size Limit. The screenshot below is of the setting you need to configure. Once you configure the new limit save the settings.