We have a TAC case open and have even attempted to repair. Supposedly CSCvc79739 and/or CSCuv95664. The repair made the upload smaller but the scheduled backup fails (well at least to date it has not succeed consistently). One of the symptoms is the uploaded file is almost exactly 1GB or 2GB - not the real size of the backup.
There is a problem with the automation as I can make a backup from the CLI with no problem.
That's a good idea about the EXPECT however - I have already written a python module to interact with Cisco routers and switches. That might be simpler than doing the REST. Thanks