If its written into files than it should be read again, try to move settings folder from app data temporary and try to read samples again and let database build and see if are there. I know there is some mentions particularly for ratings on some mediabay topics but cannot recall it, since I don’t use rating system.
If its important to you you can make your own tags for that purpose which if you have problems only with rating tags I would make custom tags for that rating, so make numbers 1 to 5 to represent ratings tag samples and see how it will translate to your system, you can add extra colums by editing defaults.xml as mr Joerg explained here: Media Bay Grouping searched items? - #19 by Grada so you can add your own rating attributes column.
In my own practice I never lose tags once I tagged samples, again I don’t use rating system so I cannot comment on that unfortunately.