Updated 09/19/19 - This fix has now been rolled out and your end users should no longer see this error.
We posted IT181632 to a limited number of customers through the Service Health Dashboard/Tenant Status Blade and are following up below with a workaround. If your end user says they see the following error message, you've likely run into this known issue (learn more will link to this post, too).
For context, the Intune legacy PC management (agent-based through the Silverlight legacy management console) does not support automatic Windows 10 feature updates, such as RS4, RS5 or 1903. However, you can manually update an Intune PC agent managed Windows 10 PC client to Windows 10, version 1903. After the update, the enrolled client loses communication with the service. On the service side, you will see that the last contact time for the client becomes stale. On the client side, when you scan for an update using Intune Center you will see this error:
Here's the workaround:
From the client side, start an elevated command prompt and run the commands below: