Notifications for Affected Service not working

Hi Experts,

I have the requirements where in If the Affected Service in the Problem Management is changed, the notification should trigger to Service Owner.

I have followed below steps to meet the requirement

Step1: Created a Field Owner and Owner Assignment in the Problem Management

Step 2:In the Link for the Device Table included both the fields in the record

The above link is helping me to get the Owner values in the Problem Ticket but the assignment Values are not coming up. 

To Test further I manually added one Owner Assignment Group in the Problem ticket and saved the records.

Step3: Created a Message record with class rc

Step 4:Created a Notification record and in the recipent option mentioned the name of Custom Assignment Field say assignmentowner in $L.file

Step 5:Created a Rule where in I am checking if Affected Service in the Current record is not equal to Affected Service in SavedRecod, then trigger the Notification

Step6:Attached the rule on all phased at AfterSuccessful Update


Now when I am trying to create a Problem Ticket and changing the Affected Service, there is no RUle getting triggered.

Kindly let me know if something is missing in the above steps