Thank you for contacting us.
I am sorry to hear you are having issues when running a backup of your site. When issues like this arise, they are usually associated with resource limitations placed on shared hosting accounts. The most notable limitations of these systems are related to Input/Output (IO), and with a site that is larger than a few hundred MB you may experience IO or CPU faults, causing backups to fail or become corrupted.
To troubleshoot the issue you are experiencing, it is recommended to speak with your host. You should be able to monitor the resources while attempting to run a backup to see if that is the cause.
Please let us know if there is anything else that we can do to assist you, we are always happy to help!