This is the repository database. It is used to track all file transfer operations in our software, the backup plans rely on this database to determine if a file needs to be uploaded to storage side.
The size of the repository depends on the number of files in the cloud(or local destination, for that matter).

You can change repository location via tools > Options > Repository menu. Make sure to launch the software as administrator when doing that.

If it's an old database and you want to clear it out you can recreate it by doing the following:
NOTE: this is a time consuming process, especially if you have millions of files on storage side

- Open Backup software and make sure there are no running plans
- In the left bottom corner right click "Backup Service" and choose "Stop Service". Do the same for RM Service if you can see it.
- After that close Backup software interface.
- Navigate to the database location: C:\ProgramData\CloudBerryLab\CloudBerry Backup\Data
- Delete "CBBackup.db"
- Launch Backup software, the repository sync process will be started automatically.
- You will need to start Backup Services back manually - the same way you stopped them.

You can monitor the progress on Welcome tab under the Storage Accounts section
When sync is complete, you can see backed up data on the Backup Storage tab and continue working with the backup.

Thanks for your answer. I'll test the procedure you told and then I'll decide what to do.