Old user name is displaying on notification tab, while the user name has been renamed

We are using confluence version 5.4.3 and crowd version 2.7.1.

When we rename a user in crowd, the changes reflects in Confluence after performing Confluence Admin> User Directories > Synchronise in Confluence.

We found that user has been renamed almost everywhere. But this is not renamed at notification tab.(Screenshot Old_Username_On_Notification_Tab.png).

For example, we have a user 'testuser2 testuser2' with user name 'testuser2'.
Now we have renamed this user from 'testuser2' to 'testuser4' and display name from 'testuser2 testuser2' to 'testuser4 testuser4'.
But this is not reflecting on Notification tab in the comment section as shown at Screenshot Old_Username_On_Notification_Tab.png.

Ideally the user name should also be changed here. Because whenever user click on username at 'testuser2 testuser2' displaying at Notification tab (Screenshot Old_Username_On_Notification_Tab.png) then it is showing that 'Page not found' page (Screenshot Page_Not_Found.png). We can see here in the screenshot 'Page_Not_Found.png' that old user name 'testuser2' is displaying on the url.

Is there any fix/workaround for this issue?