Broke screen on MacBook Pro. Purchased 4TB My Passport Ultra to back up before I take it in to get screen replaced. Set it up to mirror on my TV. Back up started and was moving fine. Went to bed, got up to find it had stopped at 71.97 GB of 92.14 GB with “33 minutes” remaining for back up. Came back one hour later and it had progressed to 72.11 with “2 hours remaining” but has stopped again. Running OS 10.12.6. Help! Thank you.
Your Mac might go into the sleep mode due to which this issue happens.
You can try changing the Energy saver settings by disabling the Sleep mode in your mac through the system preferences.
If still the issue persists, you can run first Aid on the drive to find out if there is any issue with the drive or not.