The ring at the top left shows what percentage of your devices are backed up. Below it is a short statement, for example Alles gesichert (Everything backed up) or Bitte prüfen (Please check), with the success rate. If a device missed the last backup, the statement states the number of these devices.
Devices that are turned off at night, such as notebooks, appear under Wartet auf Verbindung (Waiting for connection). This is not an error and does not trigger an alert.