I'm beginning to develop some understanding of this. I think it is not related to the changes for plugins, but rather is related to the use of click and possibly something to do with run levels.
I have put logging in /opt/mailman/mailman-bundler/venv-3.4/bin/mailman to report the command that invoked it before it in turn invokes mailman.bin.mailman.main(), and I put logging there to report the fact that control got there.
The log looks like
Tue Sep 5 15:42:57 2017 ['/opt/mailman/mailman-bundler/venv-3.4/bin/mailman', '-C', '/opt/mailman/mailman-bundler/deployment/mailman.cfg', 'stop'] Tue Sep 5 15:42:58 2017 mailman.py - main() Tue Sep 5 15:43:08 2017 ['/opt/mailman/mailman-bundler/venv-3.4/bin/mailman', '-C', '/opt/mailman/mailman-bundler/deployment/mailman.cfg', 'start', '--force'] Tue Sep 5 15:43:09 2017 mailman.py - main() Tue Sep 5 15:47:16 2017 ['/opt/mailman/mailman-bundler/venv-3.4/bin/mailman', '-C', '/opt/mailman/mailman-bundler/deployment/mailman.cfg', 'stop'] Tue Sep 5 15:48:13 2017 ['/opt/mailman/mailman-bundler/venv-3.4/bin/mailman', '-C', '/opt/mailman/mailman-bundler/deployment/mailman.cfg', 'start', '--force'] Tue Sep 5 15:58:39 2017 ['/opt/mailman/mailman-bundler/venv-3.4/bin/mailman', '-C', '/opt/mailman/mailman-bundler/deployment/mailman.cfg', 'start', '--force'] Tue Sep 5 15:58:47 2017 mailman.py - main()
The 15:42:.. entries are from a manual stop. The 15:43:.. entries are from a manual start. The 15:47:16 entry is the 'stop' from a reboot - note no 'mailman.py - main()' here, and the 15:48:13 entry is the 'start' from the reboot - again no 'mailman.py - main()' here. Finally, the 15:58:.., entries are from a manual start.
There are several 'click' decorators on the mailman.bin.mailman.main() function, and I suspect something there is detecting the run level and just quitting if a shutdown or startup is in progress.
I would like to try systemd instead, but both lists.mailman3.org and mail.python.org are on Ubuntu 14.04 which doesn't support systemd.
-- Mark Sapiro <mark@msapiro.net> The highway is for gamblers, San Francisco Bay Area, California better use your sense - B. Dylan