No route to host on port 80 but port is open

I am trying to make my nginx "status" page from machine A (Ubuntu 16.04) available from machine B (Ubuntu 20.04), but I am getting error port 80: No route to host when trying to access the page.

Both machines are connected through an internal network with addresses 10.3.1.1 and 10.3.2.201.

ping works in both directions and I have setup my nginx conf file as follows:

server {
    listen 127.0.0.1;
    listen 10.3.1.1:80;
    root /home/www/public_html;
    index index.html;

    location /basic_status {
      stub_status on;
      allow 127.0.0.1;
      allow 10.3.2.201;
      allow 10.3.1.1;
      deny all;
    }
}

For some reason I'm able to access the /basic_status page on machine A from machine A, but not from machine B:

ubuntu@machine-a:~$ curl http://10.3.1.1/basic_status
Active connections: 1
server accepts handled requests
 187325 187325 2010480
Reading: 0 Writing: 1 Waiting: 0

ubuntu@machine-a:~$ curl http://127.0.0.1/basic_status
Active connections: 1
server accepts handled requests
 187326 187326 2010481
Reading: 0 Writing: 1 Waiting: 0

ubuntu@machine-b:~$ curl http://10.3.1.1/basic_status
curl: (7) Failed to connect to 10.3.1.1 port 80: No route to host

ufw is configured on machine A to accept incoming connections to port 80 from anywhere:

ubuntu@machine-a:~$ sudo ufw status
Status: active

To                         Action      From
--                         ------      ----
80                         ALLOW       Anywhere
443                        ALLOW       Anywhere
80 (v6)                    ALLOW       Anywhere (v6)
443 (v6)                   ALLOW       Anywhere (v6)

At this this point I don't know what other setting could be causing this...