There should be a warning in the UI. In my case daily backups are not possible with Dropbox as the backup takes more than one day. I wonderd, why my backups don’t finish until I realized that a running backup will be canceled if it is slower than the backup interval.
Maybe there are better/faster services than DropBox like OneDrive, Box, Nextcloud or Seafile to include into Roon. I really like the way to store backups on a cloud drive without having a local copy.