We’ve noticed an issue with updates being installed in some iOS devices. This has been seen in devices with iOS 11.4 and higher that are in a locked state and have a passcode set. Admins may see an error in the Intune admin console when they schedule software updates for these devices and updates will not be installed.
As a workaround, end users can manually install updates on their devices from Settings > General > Software Update.
This is an iOS issue and Apple is aware of it. We’ll keep this blog post updated as we know more.