Here is a little more info. I think that I have encountered a similar problem and in my case, I believe it was because I had got in a muddle with GPG keys in the initial setup, then corrected it after the first full backup, so the backup chain was not all using the same key. It does seem to be a backup-time error that is not obvious until you try to restore.
tl;dr: do a verify after the first backup after changing any setting. (Happily I lost no data because I was only experimenting.) Hope that helps someone, -- MJR/slef My Opinion Only: see http://people.debian.org/~mjr/ Please follow http://www.uk.debian.org/MailingLists/#codeofconduct -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org