RBK50V2 Firmware 2.6.1.40 Restore from Backup Error ' Please select correct configuration file'

For some reason when I take a backup of the Orbi configuration I cannot restore that file to the same Orbi router and get the error statement: 'Please select correct configuration file'.

The file is exactly the same as the downloaded backup with no changes whatsoever.

I have tried this numerous times and with new backups - no difference!

I have have reset and factory reset the router many times in different reset methods and still no difference - always the same error message.

I have also tried another Orbi router and I get the same error statements.

I have tried vice versa backing up the other Orbi router and restore and no matter what the device mix I always get the same error statement.

It just appears that you cannot restore a backed up file no matter what options.

Can anyone offer any help to this as I cant be the only frustrated Orbi user?