I have an external tester who has received a notification that an update is available, however when they open TestFlight it doesn't have the update showing. They can still see our App within the list, it simply shows 'Open'. I have checked the build is available for the Test group, that the tester is still active in this group and that they are running the latest TestFlight version. I do see another user within that same group has successfully installed the latest version. How can I diagnose this with the user?