It's trying to load msgpack-python which has been renamed to msgpack https://github.com/borgbackup/borg/issues/3890 This is fixed upstream by https://github.com/borgbackup/borg/commit/715c3d6
I think this is a duplicate of #1630992 and FEDORA-2018-390e4ad530 ( https://bodhi.fedoraproject.org/updates/FEDORA-2018-390e4ad530 ) fixes this problem.
Ah definitely, I only looked at open bugs before filing this one, not at closed ones :) *** This bug has been marked as a duplicate of bug 1630992 ***