That indicates the Cleanup time window (8.1.11 in Administration manual) is not starting the cleanup process. The default is daily between 3 am and 4 am. If your server is turned off or sleeping during this time the UrBackup cleanup process will not run. If you changed this default, please check that the days and times you selected have been specified correctly.
[Edit to add]
If you are concerned the cleanup will take too long, you may temporarily change the Maximum backups to something closer to the current state, such as 30, and then reduce it gradually over time as automatic cleanup works to free up more space. You may need to restart the UrBackup Server process or the server computer to exit the cleanup you started manually.