Running High Sierra 10.13.6. on MacBook Pro. Time Machine stuck in performing a new backup. Message says “Waiting to Complete First Backup”. Is this an Apple problem or caused by WD MyCloud? How can I cancel/delete the in progress backup? Time Capsule will not let me select any prior backups for deletion. How do I resolve this issue?
You should make sure to check whether the My Cloud is connected or not. This error message occurred during the Time Machine backup and the My Cloud disconnects in between the process. You may reboot the My Cloud device and MacBook to start the backup process again.
However, you can contact Apple Support for more details in this concern.