Afi marks Shared (Team) drive as "Orphaned" when it doesn't have any members with Content Manager role. For example, such situation can occur if Shared drive owner had been deleted before he or she has delegated Content Manager rights to other domain users. Application needs Shared drive member with Content Manager role to impersonate under this user and download Shared drive content.
To continue backing up such Shared drive domain administrator needs to grant Content Manager role to one of the current Shared drive members or create dummy user in G Suite and then add it to this Shared drive as a Content Manager (this might be more suitable for security reasons).
How to add user with Content Manager role in the Shared drive
Log in G Suite administrator panel (https://admin.google.com), then go to the Drive and Docs settings
Dive in Manage Shared Drives section
Click on Shared drive which requires role change
Add appropriate member in pop-up window and press Send button. Shared drive access settings will be updated immediately and added user will receive email notification about access change.