Unable to see a users content or to delete the user and transfer their files

The Users & Groups section of box admin shows that I have a managed user that is using 95% of the storage of my account.  I am unable to see that content in the Content section of box admin because I don't see a Content Browser tab (in both Firefox and Microsoft Edge).  I have tried deleting the user and transferring their content to me, but when I click the Continue button it shows a busy animation and never goes to the next screen.  When I login to box admin later, no additional content has shown up in my account, and the user I tried to delete is still there and is still using 95% of the storage.

The problematic user was originally the account admin, but has an email address from a domain that box doesn't allow, so a couple years ago I created a new user (the user I'm logged is as now) and made it the admin.  I had to file ticket #2455825 to get the account reactivated.  The problematic user is now shown as Co-Admin and listed as Active, but I am unable to login using that email address.  In the Users & Groups section of box admin the icon before the name of the problematic user has a star with a purple background at the bottom-right (in contrast with my user which has a star with a blue background).