Hey,
i had found / seen an older discussion OC Updater: cURL error 60: SSL certificate problem: unable to get local issuer certificate from two years ago where an unknown user hat suggested to not use the updater app at all. Maybe this is still valid?
i had to always disable the maintenance mode on my own so i think this is an expected behavior. In seems even the manual upgrade documentation is explicitly telling you to disable the maintenance mode manually:
https://doc.owncloud.org/server/9.1/admin_manual/maintenance/manual_upgrade.html
Tom: Happy ownCloud user without updating issues since around ownCloud 9.1 by following the manual upgrade instructions.