Change how transport logs are stored.
Following this thread on the forums:
When the backup runs on cPanel it transports the site backups as it backs them up.
This means that there are multiple transport logs made for each site.
I have a lot of sites on my cPanel server.So when the transport log only stores the last 10 logs; this isn't even a full backup worth of transport logs, it makes debugging any errors impossible.
It would be good if you could change how these logs are stored.
I think it would be best if it stored all of the transport messages in the same log and rotate that every day.