The media family on device '' is incorrectly formed. SQL Server cannot process this media family

RESTORE VERIFYONLY and RESTORE DATABASE always fail immediately with this error:

Msg 3241, Level 16, State 201, Line 1
The media family on device ” is incorrectly formed. SQL Server cannot process this media family.
Msg 3013, Level 16, State 1, Line 1
VERIFY DATABASE is terminating abnormally.

The database is running with Simple recovery model and all our backup attempts are FULL backups.

DBCC CHECKDB (TheCure_CDR) is completely clean.

The BACKUP DATABASE succeeds every time. We’ve backed it up locally, remotely, single file, multi-file, with INIT, with NOINIT, and many other permutations.

RESTORE HEADERONLY succeeds every time and generates information consistent with the BACKUP DATABASE command

We’ve tried RESTORE VERIFYONLY and RESTORE DATABASE on the same computer where the backup was taken and on a different computer running the exact same version of SQL Server. This is the version:

Microsoft SQL Server 2014 (SP2-CU4) (KB4010394) – 12.0.5540.0 (X64)
Jan 27 2017 03:40:25
Copyright (c) Microsoft Corporation
Enterprise Edition (64-bit) on Windows NT 6.2 (Build 9200: ) >(Hypervisor)

A couple notable properties of our database and the circumstances:

1. The database has a defunct file group that we cannot remove. It’s been that way for years and we’ve backed up and restored many times.

2. The database has memory file groups and one memory optimized table. Again we’ve backed up and restored many times since this became the case.

3. The problem started at about the same time we upgraded the database from SP2 to SP2-CU4

4. We’ve scoured KBs and forums and have not found a single article directly on point where:

   • The database is uncorrupted
   • The backup is repeatable and always succeeds
   • The restore is on the same server where the backup was taken
   • RESTORE HEADERONLY always succeeds
   • RESTORE VERIFYONLY always fails

Has anyone seen this before?

I’ve played with the media set settings a lot because "media family" is mentioned in the error message. The defunct filegroup has three files of size zero which do not correspond to real files. I got the database into that state years ago by emptying the files then stupidly deleting them before removing them from the database. I found a number of articles directly on point saying they can’t be removed, and the only remedy is move all the data into a new database. However, it’s never caused a problem with backup/restore or even detach/attach, I’ve just ignored it.