I'm very surprised by this, and cannot duplicate your results (though I'm trying on Tumbleweed as I don't have a Leap42 install handy ... maybe time I set one up). As you say, exportfs handles this gracefully and no other code looks at /etc/exports, so I'm at a loss to find a mechanism for this failure. can you systemctl restart nfs-server and then systemctl status -l nfs-server and report the results?