SSL subdomain doesn't redirect

I am trying to visit app.example.com.

1. When I type app.example.com, it goes to example.com.
2. If I type https://app.example.com, it goes to app.example.com.

Why is the first happening?

Here's the nginx.conf

# APP =====================================================

server {
    listen 80;
    server_name app.example.com; 

    return 301 https://app.example.com$request_uri;
}

server {
    listen 443 ssl;
    server_name app.example.com;

    ssl_certificate /etc/letsencrypt/live/app.example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/app.example.com/privkey.pem;

    location / {
        proxy_pass 'http://127.0.0.1:3000';
    }
}

# WEBSITE =====================================================

server {    
    listen 80;
    server_name example.com www.example.com;

    return 301 https://example.com$request_uri;
}

server {
    listen 443 ssl;
    server_name www.example.com;

    ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem;

    return 301 https://example.com$request_uri;
}

server {
    listen 443 ssl;
    server_name example.com;

    ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem;

    location / {
        proxy_pass 'http://127.0.0.1:3002';
    }
}