Resource Locks vs. Update Deployments
An Azure 'No Delete' Resource Lock currently prevents addition or configuration of new OMS update deployments; generating an unspecified error. See Microsoft support case 117080416146171. Understanding is that in the background, creation of a new Update Deployment performs a delete action somewhere and then will bomb out and generate an error such as "This update run could not be scheduled. Please check the computer names, and try again later."
Have been told that this is not a bug, but a 'feature', so entering it here as a suggested change.