salt: 2017.7.4 to 2018.3.0 upgrade issue: Salt request timed out. The master is not responding

Description of Issue/Question

I have a standby saltmaster on saltstack 2017.7.4 and I am trying to upgrade it to 8.3.0 salt just released. After 8.3.0 upgrade, I am getting following issue.

[root@salt01 ~]# sudo salt minion01 test.version
Salt request timed out. The master is not responding. 
You may need to run your command with `--async` in order to bypass the congested event bus. 
With `--async`, the CLI tool will print the job id (jid) and exit immediately without
 listening for responses.  You can then use `salt-run jobs.lookup_jid` to look up 
the results of the job in the job cache later.
[root@salt01 ~]#

Setup

(Please provide relevant configs and/or SLS files (Be sure to remove sensitive info).)

Steps to Reproduce Issue

• snapshot salt01 VM (VMware image) for backup.
• disable /etc/yum.repos.d/salt-latest.repo
• yum update -y && reboot
• enable /etc/yum.repos.d/salt-latest.repo
• yum update -y salt && reboot
• run test.ping on all minions or just one minion

[root@salt01 ~]# sudo salt minion01 test.version
Salt request timed out. The master is not responding. 
You may need to run your command with `--async` in order to bypass 
the congested event bus. With `--async`, the CLI tool will print the job id (jid) and 
exit immediately without listening for responses. You can then 
use `salt-run jobs.lookup_jid` to look up the results of the job in the job cache later.
[root@salt01 ~]#

• If I revert the salt01’s VM image back to saltstack 7.4 version. this problem disappear.

Versions Report

• errors in systemctl status -l salt-master.

[root@salt01 ~]# systemctl status -l salt-master
? salt-master.service - The Salt Master Server
   Loaded: loaded (/usr/lib/systemd/system/salt-master.service; enabled; vendor preset: disabled)
   Active: active (running) since Wed 2018-04-04 09:08:33 CDT; 19min ago
     Docs: man:salt-master(1)
           file:///usr/share/doc/salt/html/contents.html
           https://docs.saltstack.com/en/latest/contents.html
 Main PID: 1090 (salt-master)
   CGroup: /system.slice/salt-master.service
           +-1090 /usr/bin/python /usr/bin/salt-master
           +-1480 /usr/bin/python /usr/bin/salt-master
           +-1707 /usr/bin/python /usr/bin/salt-master
           +-1708 /usr/bin/python /usr/bin/salt-master
           +-1715 /usr/bin/python /usr/bin/salt-master
           +-1716 /usr/bin/python /usr/bin/salt-master
           +-1717 /usr/bin/python /usr/bin/salt-master
           +-1718 /usr/bin/python /usr/bin/salt-master
           +-1724 /usr/bin/python /usr/bin/salt-master
           +-1726 /usr/bin/python /usr/bin/salt-master
           +-1727 /usr/bin/python /usr/bin/salt-master
           +-1728 /usr/bin/python /usr/bin/salt-master
           +-1729 /usr/bin/python /usr/bin/salt-master
           +-1730 /usr/bin/python /usr/bin/salt-master

Apr 04 09:12:15 salt01 salt-master[1090]: pub = salt.crypt.get_rsa_pub_key(pubfn)
Apr 04 09:12:15 salt01 salt-master[1090]: File "/usr/lib/python2.7/site-packages/salt/crypt.py", line 210, in get_rsa_pub_key
Apr 04 09:12:15 salt01 salt-master[1090]: key = RSA.load_pub_key(path)
Apr 04 09:12:15 salt01 salt-master[1090]: File "/usr/lib64/python2.7/site-packages/M2Crypto/RSA.py", line 406, in load_pub_key
Apr 04 09:12:15 salt01 salt-master[1090]: return load_pub_key_bio(bio)
Apr 04 09:12:15 salt01 salt-master[1090]: File "/usr/lib64/python2.7/site-packages/M2Crypto/RSA.py", line 422, in load_pub_key_bio
Apr 04 09:12:15 salt01 salt-master[1090]: rsa_error()
Apr 04 09:12:15 salt01 salt-master[1090]: File "/usr/lib64/python2.7/site-packages/M2Crypto/RSA.py", line 302, in rsa_error
Apr 04 09:12:15 salt01 salt-master[1090]: raise RSAError, m2.err_reason_error_string(m2.err_get_error())
Apr 04 09:12:15 salt01 salt-master[1090]: RSAError: no start line
[root@salt01 ~]#

• version report

[root@salt01 ~]# salt --versions-report
Salt Version:
           Salt: 2018.3.0

Dependency Versions:
           cffi: 1.6.0
       cherrypy: unknown
       dateutil: 1.5
      docker-py: Not Installed
          gitdb: 0.6.4
      gitpython: 1.0.1
          ioflo: 1.3.8
         Jinja2: 2.7.2
        libgit2: 0.24.6
        libnacl: 1.4.3
       M2Crypto: 0.21.1
           Mako: 0.8.1
   msgpack-pure: Not Installed
 msgpack-python: 0.5.1
   mysql-python: 1.2.5
      pycparser: 2.14
       pycrypto: 2.6.1
   pycryptodome: 3.4.3
         pygit2: 0.24.2
         Python: 2.7.5 (default, Aug  4 2017, 00:39:18)
   python-gnupg: Not Installed
         PyYAML: 3.11
          PyZMQ: 15.3.0
           RAET: Not Installed
          smmap: 0.9.0
        timelib: 0.2.4
        Tornado: 4.2.1
            ZMQ: 4.1.4

System Versions:
           dist: centos 7.4.1708 Core
         locale: UTF-8
        machine: x86_64
        release: 3.10.0-693.21.1.el7.x86_64
         system: Linux
        version: CentOS Linux 7.4.1708 Core

[root@salt01 ~]#