Update note on assignmentType property behavior

Clarified behavior of assignmentType property during custom policy assignments.

Author: MutemwaRMasheke

articles/governance/machine-configuration/concepts/assignments.md

@@ -34,6 +34,9 @@ resource type is `Microsoft.GuestConfiguration/guestConfigurationAssignments`. A
 the **complianceStatus** property of the guest assignment resource to report compliance status. For
 more information, see [getting compliance data][02].
 
+> [!NOTE]
+> When assigning a custom policy that deploys a guest configuration, the assignmentType property on the guest assignment resource may temporarily appear as "Null" before being updated to reflect the value specified in the policy definition. This is expected behavior and typically resolves within one hour.
+
 ### Deletion of guest assignments from Azure Policy
 
 When an Azure Policy assignment is deleted, if the policy created a machine configuration