Full Disk Access is enabled, but com.apple.mail/Data complains

[sjmills]

I have both RetrospectInstantScan and RetrospectEngine added and turned on in my Privacy prefs. Retrospect runs on the same machine it backs up, so no client needed. After last night's backup I see in the log:

While scanning volume TubeDrive,
        Folder /Volumes/TubeDrive/Users/myname/Library/Containers/com.apple.mail/Data/,
            Retrospect has detected it is not listed under "Full Disk Access" on the backup source system 
                and cannot access all user data to create a complete backup. Please follow our step-by-step guide: 
               https://www.retrospect.com/kb/macos_full_disk_access

Well, it's on, so what's its problem?

Retrospect 15.6.0 (125)

macOS 10.14.1 (18B75)

[Lennart_T]

Is TubeDrive your boot drive?

Does the problem persist after a safe boot (and a normal boot after that)?

[sjmills]

Yes, it's my boot drive.

Safe boot and regular boot did not make a difference. Same error last night. I wonder if Apple added another level of folders or changed the permissions on Data, since the Retrospect doc lists ~/Library/Containers/com.apple.mail/, but not ~/Library/Containers/com.apple.mail/Data.