Update async-cascading.md

Author: NHelgren

power-platform/admin/async-cascading.md

@@ -123,6 +123,11 @@ If the job runs successfully, the merge assigns all the related contacts and the
 
 If during the record merge process another user deletes a related contact record, but order records still exist related to the contact record, the merge job will fail because a parent to a child record is missing. If you choose to skip the parenting check during the record merge, the orders with the missing contact record will be merged into the target account record. However, no related contact records will be assigned to the target account and the job will complete.
 
+#### Merge causing locks that prevent other access changes
+    
+The Cascade Merge operation grants access to the new owner of the subordinate entity. To do this, it accesses the Principal Object Table and makes changes to the Principal Object Access table which requires a lock. If a merge operation contains many records (based on the cascade relationship), this lock could be in place for an extended amount of time. This could result in an error if an operation attempts to grant/revoke access of an unrelated record while the merge is running. If this occurs, try executing the merge in off hours so the blocking can be reduced.
+
+
 ### See also
 
 [Entity relationships overview](/powerapps/maker/common-data-service/create-edit-entity-relationships)