If something is not working properly is strongly recommended to check first the Debug Logs for a better investigation
Go to “General Settings” tab and on Debug section choose a deeper log activity tracking, such as “Almost Everything”.
Go to System -> Admin Logs page and check all stored Logs. You may wanna Clean Up all Logs before starting your investigated process (Backup, Restore, etc).
Check what was the latest stored Log to identify where and why the process was stopped.