For what ever reason the plugin is not ignoring its data file.
The file .sc_wpfmp_scan_data is where where this plugin stores the data from the past scan to compare to the new scan so it can tell when files change.
The file size of this file will will be however big it needs to store the previous scan. I would expect the file size to increase over time as your website grows. The more images you upload the more files this plugin has to scan and the more files that have to be recorded in the data file.
You can safely ignore the data files changing as they will each time the plugin scans. The plugin should automatically ignore the scan files but in your cases it is not… I’m not sure why.
As flashbuddy says above you can ignore the scan data folder in the settings and this will stop you getting notifications that the data file has changed each time.
I’m currently doing work on this plugin that does away with storing the data files in the filesystem hopefully removing the problems that you are all having. I’m working on it bit by bit in my spare time so I don’t have a time frame when it will be ready.