Have to confess (sorry, sometimes seeing is knowing where to go/try next) ... tried running your cron remotely and it said backups weren't scheduled. It did, however, complete. I ran the cron in what appears to be non-prime time for your location. Running cron and scheduling something heavy on processing (like auto backups) during 'prime time' for other server processes, is something that might cause things to fail.
Check scheduling of everything. Not only Moodle, but OS/Server.
The backup process still needs a temporary area in which to build backup files. Check your operating system temp variable and whatever that's set to check the folder being used. Check to see if what is written to that temp area can be copied back into moodledata/filedir/
Check php.ini settings for things related to temp.
'spirit of sharing', Ken