@BKrishna As far as I know, when a correspondence with "after create = send" option could not be send appropriately, pega routes the case to the originator's manager. You can check the logs to find out what caused email sending failure.
I figured out a way to resolve this issue, I am not sure this could be the proper way of resolving the issue, but it worked for me in two scenarios. First scenarios neither Customer nor Approver is unable to see the Case ID in their worklist , 2nd scenarios when a Customer clicks on Case ID, he is getting an error "You are authorized..."
1. Click on the Assign-Worklist class, we can see the list list of Cases, search our Case ID.
2. Open the Case ID which is having the proper Flow Name, we can ignore the cases which are showing as FixCorrespondence
3. Case ID gets opened in XML, note down the value in notepad which is in pxAssignedOperatorID tag (OR) pzInsKey tag both are same.
4. Run the Pega OOTB Activity "pxTransferAssignment" which will ask three parameters 1. pxAssignedOperatorID or pzInsKey value without quotation 2nd paramter worklist and the 3rd parameter to whom we need to route the assignment that person Operator ID, Run the activity, we will get one error, we can ignore that error. Now, we could see the assignment gets routed to appropriate person.