In the Kubic logs I found:

[ERROR   ] Function network.default_route in mine_functions failed to execute


So I tried:
# salt-call --local network.default_route
[ERROR   ] An un-handled exception was caught by salt's global exception
handler:
AttributeError: module 'salt.ext' has no attribute 'ipaddress'
Traceback (most recent call last):
  File "/usr/bin/salt-call", line 11, in <module>
    salt_call()
  File "/usr/lib/python3.6/site-packages/salt/scripts.py", line 400, in
salt_call
    client.run()
  File "/usr/lib/python3.6/site-packages/salt/cli/call.py", line 57, in run
    caller.run()
  File "/usr/lib/python3.6/site-packages/salt/cli/caller.py", line 134, in run
    ret = self.call()
  File "/usr/lib/python3.6/site-packages/salt/cli/caller.py", line 212, in call
    ret['return'] = func(*args, **kwargs)
  File "/usr/lib/python3.6/site-packages/salt/modules/network.py", line 1662,
in default_route
    _routes = routes()
  File "/usr/lib/python3.6/site-packages/salt/modules/network.py", line 1619,
in routes
    routes_ = _ip_route_linux()
  File "/usr/lib/python3.6/site-packages/salt/modules/network.py", line 518, in
_ip_route_linux
    address_mask = convert_cidr(comps[0])
  File "/usr/lib/python3.6/site-packages/salt/modules/network.py", line 1143,
in convert_cidr
    network_info = salt.ext.ipaddress.ip_network(cidr)
AttributeError: module 'salt.ext' has no attribute 'ipaddress'

This works fine on SLES12 SP3.
salt is the latest from
https://build.opensuse.org/package/show/systemsmanagement:saltstack:testing/salt