Sorry for the late Answer. I had lots of work last week. I tried again but got stuck on restarting 'mailman-web'. There is a '/var/run/mailman3/web/ directory which is empty and the log reports a different directory for the pid file:
writing pidfile to /run/mailman3-web/mailman3-web.pid
open("/run/mailman3-web/mailman3-web.pid"): No such file or directory
[core/utils.c line 3590]
Markus
