[MM3-users] admin/login/ cannot be accessed

Ubuntu 20.04 python3-django 2:2.2.6-1ubuntu1 python3-django-hyperkitty 1.3.1 (built from sources) mailman3-full 3.2.2-1

Nginx server configuration:

...
	########
        # Static
	########
        location /favicon.ico
        {
                alias <mysite_dir>/static/hyperkitty/img/favicon.ico;
        }
        location /static/favicon.ico
        {
                alias <mysite_dir>/static/postorius/img/favicon.ico;
        }
        location /static/ 
        {
                alias <mysite_dir>/static/;
        }

	#######################
        # Upstream uwsgi server
	#######################
        location / 
        {
                include /etc/nginx/uwsgi_params;
                uwsgi_pass 127.0.0.1:<uwsgi_server_port>;
        }
...

where:

• is a symlink to /static
• matches the one defined in /etc/mailman3/uwsgi.ini:

[uwsgi]
# Port on which uwsgi will be listening.
uwsgi-socket = 127.0.0.1:<uwsgi_server_port>

All 3 systemd services run fine:

• mailman3
• mailman3-web
• qcluster

I'm trying to login to the django administration pages. I get the django administration login page at: https://mysite/admin/login/ Logging in with the admin credentials leads to:

This site can’t be reached
The webpage at https://mysite/admin/login/ might be temporarily down or it may have moved permanently to a new web address.
ERR_HTTP2_PROTOCOL_ERROR

This is very strange because it is the URL which I used to get the login page in the first place.

If I launch a test web server at another port with:

<django_dir># python3 manage.py runserver <mysite_ip_address>:8080
Performing system checks...

System check identified no issues (0 silenced).
December 11, 2019 - 17:50:48
Django version 2.2.6, using settings 'settings'
Starting development server at http://<mysite_ip_address>:8080/
Quit the server with CONTROL-C.

and access it at http://<mysite_ip_address>:8080/admin/login/ to login with the same credentials as before, I get through and all the django administration lines appear, although in a degraded layout:

Site administration
Accounts
Email addresses	Add	Change
Authentication and Authorization
Groups	Add	Change
Users	Add	Change
Django Mailman 3
Mail domains	Add	Change
Profiles	Add	Change
...

Any idea what could be happening here?