nginx - redirect only main domain to www, not subdomains

Question

I'm new to Nginx and trying to figure out how to properly handle subdomains. What I want to achieve is that the main domain example.com is always redirected to https://www.example.com, but subdomains as sub.example.com should always be redirected to https://sub.example.com. In my current setup the first requirement is fulfilled, but sub.example.com always gets redirected to https://www.sub.example.com. What is the problem with my configuration and how can I fix it?

Thanks in advance, Fabian.

---

My two server config files:

default

server {
    listen 80;
    listen [::]:80;
    server_name example.com www.example.com;
    return 301 https://www.$host$request_uri;
}

server {
    listen 443 ssl http2;
    server_name example.com;
    ssl_certificate /path/on/my/server/to/certificate.pem;
    ssl_certificate_key /path/on/my/server/to/privatekey.pem;
    return 301 https://www.$host$request_uri;
}


server {
    listen 443 default_server ssl http2;
    listen [::]:443 default_server ssl http2;
    server_name www.example.com;
    ssl_certificate /path/on/my/server/to/certificate.pem;
    ssl_certificate_key /path/on/my/server/to/privatekey.pem;

    root /var/www/html;
    index index.html index.htm index.nginx-debian.html;

    location / {
        try_files $uri $uri/ =404;
        index index.php index.html index.htm;
    }
}

sub

server {
    listen 80;
    listen [::]:80;
    server_name sub.example.com;
    return 301 https://$host$request_uri;
}

server {

    listen 443 ssl;
    listen [::]:443 ssl;
    server_name sub.example.com;
    ssl_certificate /path/on/my/server/to/subcertificate.pem;
    ssl_certificate_key /path/on/my/server/to/subprivatekey.pem;

    root /var/www/sub;

    location / {
        index index.php index.html index.htm;
        try_files $uri = 404;
    }

    location ~ \.php$ {
        try_files $uri = 404;
        include fastcgi_params;
        fastcgi_pass unix:/var/run/php7-fpm-web1.sock;
        fastcgi_index index.php;
        fastcgi_param SCRIPT_FILENAME $document_root/$fastcgi_script_name;
    }
}

Answer 1

If this problem happens to anyone else: Try to clean your browser cache.