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.
Based on the screenshot you provided it looks like the backups for your website are almost 4GB, which can lead to problems creating backups by using a plugin. You also might have better luck using a server level backup solution from your hosting provider since they can generally handle more than a website based solution.
I hope your host is able to figure out where there problems are occurring and please let us know if there is anything else that we can do to help!