This can happen if your iCloud database is quite large or you save to it in rapid succession. What happens when you save (using any client) is that the Apple iCloud sync system has to upload it to iCloud in the background and this can take some time. It may take a few minutes. When you save another version of the database before this process finishes, the iCloud system creates another version of the file and appends "1", "2", "3" etc. Strongbox will automatically detects these files and add them to your database list, if they are in the Strongbox iCloud folder.
This means what you are seeing is a sync problem, because of how slow iCloud is to sync. Strongbox cannot control this, nor can any other client, this is a slow Apple iCloud sync issue.
Recommended Solution
If you will be repeatedly and rapidly updating this database file, we'd recommend another cloud provider. There are many to choose from, Dropbox, Google Drive, OneDrive, WebDAV (e.g. Nextcloud), SFTP (your own server). For each of these, Strongbox has direct control over the sync process and can manage multiple versions saved rapidly.
Strongbox has native support for all of these cloud drives on iOS and macOS, so you don't need to install a third party app and there will be no sync issues.
Alternative Solutions
Other things you can do to help, is to reduce the size of your database, make sure you are on a very fast connection, and not rapidly save different versions of the database in quick succession.