If you deploy an Azure Conditional Access policy to require all Windows PC’s to be domain joined, you may find that Azure AD Connect no longer synchronizes.
And during an upgrade to the latest version of Azure AD Connect, you may be prompted with the error message “System.InvalidOperationException: Showing a modal dialog box or form when the application is not running in UserInteractive mode is not a valid operation.”
To resolve this, modify the conditional access policy to exclude the Azure AD Connect Service Account, which can be found by searching for “On-premises directory synchronization service account”
Then create a second conditional access policy that is targeted this same on-prem account with a condition exclusion for all trusted locations, and a block rule for all other access. This effectively creates an IP-Fence that prevents this service account from logging in from anything other than the trusted location.