This is caused by an upstream change. See https://github.com/saltstack/salt/issues/54871.

Upgraded through pkg, using latest repo (as opposed to quarterly). I'm using py27-salt, though I assume py36-salt is also affected. Saltstack minion refuses to start now. I assume master is also affected. The error:

---
 ~ » sudo service salt_minion start
Starting salt_minion.
Traceback (most recent call last):
  File "/usr/local/bin/salt-minion", line 6, in <module>
    from pkg_resources import load_entry_point
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 3250, in <module>
    @_call_aside
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 3234, in _call_aside
    f(*args, **kwargs)
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 3263, in _initialize_master_working_set
    working_set = WorkingSet._build_master()
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 585, in _build_master
    return cls._build_from_requirements(__requires__)
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 598, in _build_from_requirements
    dists = ws.resolve(reqs, Environment())
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 786, in resolve
    raise DistributionNotFound(req, requirers)
pkg_resources.DistributionNotFound: The 'PyYAML<5.1' distribution was not found and is required by salt
/usr/local/etc/rc.d/salt_minion: WARNING: failed to start salt_minion
---

py-yaml was upgraded to 5.1 in June in FreeBSD. Saltstack worked fine until now. Maybe the requirements can be patched until upstream fixes it?

Reported on Github, too.