[BUG] Cannot start multiple minions on the same machine

Description
The docs imply that you can run multiple minions on the same machine by specifying different config to the salt-minion process (https://docs.saltstack.com/en/master/ref/configuration/minion.html#std-conf_minion-id). I recall this working on 3000.x but I am unable to get it working on 3001.1

Setup
Create separate config location and files, e.g.

# /etc/salt/another-minion/minion.d/minion.conf

id: another-minion

Steps to Reproduce the behavior
Be sure to have another minion running on the same machine. Start the second minion with salt-minion -c /etc/salt/another-minion

Expected behavior
Both minions should start and operate successfully. Instead, I am currently getting the following error:

[INFO    ] Setting up the Salt Minion "another-minion"
[INFO    ] An instance is already running. Exiting the Salt Minion
[INFO    ] Shutting down the Salt Minion
The Salt Minion is shutdown.

Versions Report

Salt Version:
           Salt: 3001.1

Dependency Versions:
           cffi: 1.14.1
       cherrypy: Not Installed
       dateutil: Not Installed
      docker-py: 4.2.0
          gitdb: Not Installed
      gitpython: Not Installed
         Jinja2: 2.11.2
        libgit2: Not Installed
       M2Crypto: 0.35.2
           Mako: Not Installed
   msgpack-pure: Not Installed
 msgpack-python: 0.6.2
   mysql-python: Not Installed
      pycparser: 2.20
       pycrypto: 2.6.1
   pycryptodome: Not Installed
         pygit2: Not Installed
         Python: 3.6.8 (default, Apr  2 2020, 13:34:55)
   python-gnupg: Not Installed
         PyYAML: 5.3.1
          PyZMQ: 19.0.1
          smmap: Not Installed
        timelib: Not Installed
        Tornado: 4.5.3
            ZMQ: 4.3.2

System Versions:
           dist: centos 7 Core
         locale: UTF-8
        machine: x86_64
        release: 3.10.0-1127.el7.x86_64
         system: Linux
        version: CentOS Linux 7 Core

Start with the documented command, salt-minion -c /etc/salt/another-minion, alongside an existing minion, then trace the instance-running check that produces the reported exit. Compare how the separate config locations and minion IDs are handled; done means both configured minions start and operate successfully on the same machine.