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I see two problems in this log file.

The first problem is that the PHP memory limit is 32 Megabytes which is pretty low. The minimum part of Joomla we need to load to run a CLI application is 8MB as you can see in the log which leaves barely 24 Mb for the backup to run. This is the absolutely minimum amount of memory we need and may not be enough for a larger site. Seeing the size of the tables you are backing up I am inclined to believe that you will need more memory than that. Please ask your host to edit the php.ini for the PHP CLI binary and increase the memory_limit to at least 64M.

The second problem I see is that the backup is killed at exactly 32 seconds wall clock elapsed time. This is about 30 seconds of CPU time on the main backup thread when I take into account the number of database queries already executed. This means that most likely your backup is killed by the operating system because there's a CPU usage limit set to 30 seconds, the default value for cPanel installations. You can tell your host to edit the /etc/security/limits.conf file on the server and increase your user's CPU usage limit to something that's enough for the backup to complete. If you are not sure what would be enough, take a backup through the site's backend, go to Manage Backup page and see the time elapsed for the backup. That's how long the CPU usage limit needs to be.