Hi,
SMTape is a block by block copy of the file system associated with a particular version of Data ONTAP; therefore, when you retrieve data from tape, the destination of the retrieval must use the same or later version of Data ONTAP used when storing data to tape. Here, the 'later' is actually suggesting a compatible SnapMirror ONTAP version.
Cause : You can restore data to volumes created across up to two major consecutive ONTAP releases only. For 9.1: it would be 9.1.9.2 & 9.3 only.
Compatible ONTAP versions for SnapMirror relationships:
https://docs.netapp.com/ontap-9/index.jsp?topic=%2Fcom.netapp.doc.pow-dap%2FGUID-0810D764-4CEA-4683-8280-032433B1886B.html
Workaround: hmm...may be restore it to 9.1 itself, and then NDMPCOPY to 9.7, NDMP doesn't care about disk-geometry or underneath file-system version.
Thanks!