Nginx stops after a while without registering any trackable log

I have a server (Ubuntu 20.04) that uses Nginx as a web server. Also, several projects are on it. The problem is, sometimes the Nginx fails (stops). Like this:

I really have no idea why it crashes. Searched a lot for it and made some changes in the server blocks (port listening), but still it stops sometimes. The important part is, when I run systemctl restart nginx it back to be working as well, but after a while, fails again.

The result of 10 last lines inside the nginx error log:

2023/03/17 06:54:46 [emerg] 88675#88675: bind() to 0.0.0.0:443 failed (98: Address already in use)
2023/03/17 06:54:46 [emerg] 88675#88675: bind() to 0.0.0.0:80 failed (98: Address already in use)
2023/03/17 06:54:46 [emerg] 88675#88675: bind() to [::]:80 failed (98: Address already in use)
2023/03/17 06:54:46 [emerg] 88675#88675: bind() to 0.0.0.0:443 failed (98: Address already in use)
2023/03/17 06:54:46 [emerg] 88675#88675: bind() to 0.0.0.0:80 failed (98: Address already in use)
2023/03/17 06:54:46 [emerg] 88675#88675: bind() to [::]:80 failed (98: Address already in use)
2023/03/17 06:54:46 [emerg] 88675#88675: bind() to 0.0.0.0:443 failed (98: Address already in use)
2023/03/17 06:54:46 [emerg] 88675#88675: still could not bind()
2023/03/17 06:54:48 [error] 88631#88631: MEMSTORE:19: my procslot not found! I don't know what to do!
nginx: worker process: /build/nginx-lUTckl/nginx-1.18.0/debian/modules/nchan/src/store/memory/memstore.c:1616: nchan_store_exit_worker: Assertion `0' failed.

And this is the /etc/nginx/sites-enabled/default content:

server {    
    server_name api5.arshiyaniha.com;
    root /var/www/html/api/public/ ;

    error_log /var/log/nginx/api-new-error.log ;
    access_log /var/log/nginx/api-new.log ;

    index index.php index.html index.htm index.nginx-debian.html ;

    if ($request_uri ~* "^(.*/)index\.php$") {
       return 301 $1;
    }

    location / {
       try_files $uri $uri/ /index.php?$query_string;
    }

    location ~ \.php$ {
        include snippets/fastcgi-php.conf;
        fastcgi_pass unix:/run/php/php8.1-fpm.sock;
        fastcgi_read_timeout 2000;
    }

    listen [::]:443 ssl ipv6only=on; # managed by Certbot
    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/api5.arshiyaniha.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/api5.arshiyaniha.com/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

}


server {
        server_name arshiyanadmin.arshiyaniha.com;
        root /var/www/html/panel-front/build/ ;

        error_log /var/log/nginx/arshiyanadmin.log ;
        access_log /var/log/nginx/arshiyanadmin.log ;

        index index.html;

        location / {
           try_files $uri $uri/ /index.html?$query_string;
        }

    client_max_body_size 10M;

    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/arshiyanadmin.arshiyaniha.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/arshiyanadmin.arshiyaniha.com/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

}

server { 
     server_name api.arshiyaniha.com;
     location / {
          proxy_pass http://localhost:4020;
          proxy_http_version 1.1;
          proxy_set_header Upgrade $http_upgrade;
          proxy_set_header Connection 'upgrade';
          proxy_set_header Host $host;
          proxy_cache_bypass $http_upgrade;
     }

    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/api.arshiyaniha.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/api.arshiyaniha.com/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

}

server {
     server_name dashboardapi.arshiyaniha.com;
     location / {
          proxy_pass http://localhost:4021;
          proxy_http_version 1.1;
          proxy_set_header Upgrade $http_upgrade;
          proxy_set_header Connection 'upgrade';
          proxy_set_header Host $host;
          proxy_cache_bypass $http_upgrade;
          proxy_connect_timeout 60s;
          proxy_read_timeout 5400s; 
          proxy_send_timeout 5400s;
    }

    listen 443 ssl; # managed by Certbot 
    ssl_certificate /etc/letsencrypt/live/dashboardapi.arshiyaniha.com/fullchain.pem; # managed by Certbot 
    ssl_certificate_key /etc/letsencrypt/live/dashboardapi.arshiyaniha.com/privkey.pem; # managed by Certbot 
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot 
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

}

server { 
     server_name files.arshiyaniha.com;
     location / {
          proxy_pass http://localhost:4022;
          proxy_http_version 1.1;
          proxy_set_header Upgrade $http_upgrade;
          proxy_set_header Connection 'upgrade';
          proxy_set_header Host $host;
          proxy_cache_bypass $http_upgrade;
     }

    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/files.arshiyaniha.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/files.arshiyaniha.com/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot
}

server {
    if ($host = api.arshiyaniha.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot
 
    server_name api.arshiyaniha.com;
    listen 80;
    return 404; # managed by Certbot
}

server {
    if ($host = files.arshiyaniha.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot

    server_name files.arshiyaniha.com;
    listen 80;
    return 404; # managed by Certbot

}

server {
    if ($host = dashboardapi.arshiyaniha.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot

    server_name dashboardapi.arshiyaniha.com;
    listen 80;
    return 404; # managed by Certbot
}

server {
    if ($host = arshiyanadmin.arshiyaniha.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot
   
    server_name arshiyanadmin.arshiyaniha.com;
    listen 80;
    return 404; # managed by Certbot
}


server {
    if ($host = api5.arshiyaniha.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot

    listen 80;
    listen [::]:80;    

    server_name api5.arshiyaniha.com;
    return 404; # managed by Certbot
}

Any idea what's the exact problem and how can I fix it?

This sounds like a 4 year old bug. Although it has been marked as resolved. It's possible it hasn't been backported into your OS.

And I know this isn't the solution, but as a workaround, you can configure systemd to restart nginx automatically on failure.

Create new directory,

mkdir /etc/systemd/system/nginx.service.d/

Create new file

nano /etc/systemd/system/nginx.service.d/override.conf

Paste following content

[Unit]
StartLimitIntervalSec=500
StartLimitBurst=5

[Service]
Restart=on-failure
RestartSec=5s

Now restart daemon service and nginx.

Try it.