After further debugging and discussion i bring this back here because i think it is related to the debian packages.
Summary: I figured out that a restart/stop-start of mailman3-suite and mailman3- core does not stop mailman. 'service mailman3-suite stop' kills only the uwsgi processes (not mailman) this is why the changed config is not active for the webUI after stop- start mailman in this way. a 'mailman stop' and 'mailman start' seems to work Details: https://gitlab.com/mailman/mailman/issues/455
