Yes this is my problem too, updates not being completed can be affected by battery percentage of the device: they need to have more than 50% battery, have enough free space for the update and not be in power save mode. On shared devices they need to be logged out of the session.
I am from Cape Town in South Africa and have Load Shedding, so often devices do not charge enough overnight due to the power being off and thus updates or device backups do not happen.
There is an option to set auto logout on the Automated Device Enrollment Profile. Note: after changing it, you will need to reset the affected shared iPads and reenroll them:
