Comment # 6 on bug 964347 from Neil Brown

I haven't found anything....
I tried it myself and the filesystem stayed mounted, so maybe I have a
different version of something installed ... or something.

My best guess is that wicked is trying to be clever when the network interface
goes down - you are using wicked I assume (ps axgu | grep wicked).  It might be
possible to configure tumbleweed to use network-manager instead.

Does
  grep -ri nfs /etc/sysconfig/network
  grep -ri mount /etc/sysconfig/network

show anything interesting?  That is where a wicked config file would be.

If that doesn't show anything, could you
 systemd-analyze set-log-level 7
then suspend, then
 journalctl -p 7 -xb

and collect any systemd log messages during syspend/resume.  Maybe that will
shed some light.