If you see a blank display when selecting an Account Group, removing and recreating the Account Group will likely solve the issue.
To do this, go to File | New | Account Group to create a new one, and drag each of your accounts out of the old account group and drop them into the new one. Once you have your accounts moved into the new group, you can delete the old one by right-clicking on it (or Control + Click on Mac), and selecting Delete.