Sporadic KeyError: 'runner' in reactor

[marbx]

Description of Issue/Question

A salt-master has only one runner that reacts on the minion_ping event of 3000 client..

The runner works fine, but there are sporadic errors in /var/log/salt/master like the one below

What does this error mean?

2019-05-10 05:41:54,280 [salt.utils.reactor:423 ][ERROR   ][22195] Reactor 'minion_ping_reaction' failed to execute runner 'minion_ping_runner.main'
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/salt/utils/reactor.py", line 391, in run
    react_fun = self.client_cache[low['state']].functions.get(low['fun'])
  File "/usr/lib/python2.7/site-packages/salt/utils/cache.py", line 70, in __getitem__
    return dict.__getitem__(self, key)
KeyError: u'runner'

Versions Report

Salt Version:
Salt: 2018.3.4

Dependency Versions:
cffi: Not Installed
cherrypy: Not Installed
dateutil: Not Installed
docker-py: Not Installed
gitdb: Not Installed
gitpython: Not Installed
ioflo: Not Installed
Jinja2: 2.7.2
libgit2: Not Installed
libnacl: Not Installed
M2Crypto: Not Installed
Mako: Not Installed
msgpack-pure: Not Installed
msgpack-python: 0.5.6
mysql-python: 1.2.5
pycparser: Not Installed
pycrypto: 2.6.1
pycryptodome: Not Installed
pygit2: Not Installed
Python: 2.7.5 (default, Apr 9 2019, 14:30:50)
python-gnupg: Not Installed
PyYAML: 3.11
PyZMQ: 15.3.0
RAET: Not Installed
smmap: Not Installed
timelib: Not Installed
Tornado: 4.2.1
ZMQ: 4.1.4

System Versions:
dist: centos 7.6.1810 Core
locale: UTF-8
machine: x86_64
release: 3.10.0-957.5.1.el7.x86_64
system: Linux
version: CentOS Linux 7.6.1810 Core

Minions are 2016 Windows

[garethgreenaway]

@markuskramerIgitt Thanks for the report. Can you provide the contents of the reactor in question that is producing these messages?

[marbx]

The reactor has just 4 lines, apart from the comments

# /srv/salt/reactor/minion_ping_reactor.sls (Yaml syntax)
#

minion_ping_reaction:
  runner.minion_ping_runner.main:
    - arg:
      - {{ data }}

[marbx]

@garethgreenaway I assume KeyError: u'runner' refers to runner.minion_ping_runner.main?

[marbx]

@garethgreenaway, do you need more input?

[marbx]

2 times a week
I can neglect that