by Ken Task.
First ... "Moodle US Support" ... a Moodle Partner ... so don't take for gospel anything I suggest here.
From what I understand about load balancers - all nodes should point to the same moodledata directory.
To the best of my knowledge, process is:
a backup (.mbz) file is built first ... moodledata/temp/backup/ using a slightly different folder name ... guess it ids something.
From there it's restored - which means whatever is contained in it gets spread across moodledata/filedir/ and tables in DB are updated/added, then that temp 'spooling area' removed ... so you have to catch it at a fail or monitor and watch in realtime what goes on there.
Cron job one server ... there is a poster here in these forums that has done something like that ... setup another moodle server that's not a node in load balancer and it had just enough core code to run the cron from there. Think he used commercial RedHat ... if that makes a diff.
Anyhoo, hopefully, someone who runs a load bal setup (and those also could have some quirks of their own) has discovered same issue and would be kind enough to share what they did to solve!
Best of luck! (if there is such a thing!)
'SoS', Ken