The incremental backup fails and instead a full backup is performed as seen below (GET /previous: 400 Bad Request)
2021-08-20T14:40:01+02:00: starting new backup on datastore 'foo-1': "host/foo/2021-08-20T12:40:01Z"
2021-08-20T14:40:01+02:00: download 'index.json.blob' from previous backup...
