i updated to the latest version 4.7.3 and it was 4.7.1 i believe.

i think everything is causing from FastCGI. because, any changes i make in the second site is not applying, but it works when i disable FastCGI. but no problem with the main site even with FastCGI.
so what should i look in to now?

@hansen
i just find out everything is from FastCGI. my site acts strangely when FastCGI is turned on. seems all the pages inside wp-admin area are also being cached in fastCGI. i restored my droplet from earlier point, disabled FastCGI and updated wordpress without any issue. also all strange things are also gone when i disabled FastCGI.

could you tell me where i have done wrong setting up FastCGI?

Here is my FastCGI setup just like described in DO tutorial

fastcgi_cache_path /var/run/cache levels=1:2 keys_zone=MYAPP:100m inactive=60m;
fastcgi_cache_key "$scheme$request_method$host$request_uri";
add_header X-Cache $upstream_cache_status;
fastcgi_ignore_headers Cache-Control Expires Set-Cookie;

        #Cache everything by default
       set $no_cache 0;

        #Don't cache POST requests
       if ($request_method = POST) {
               set $no_cache 1;
       }

        #Don't cache if the URL contains a query string
       if ($query_string != "") {
               set $no_cache 1;
       }

        #Don't cache the following URLs
       if ($request_uri ~* "/wp-admin/|/xmlrpc.php|wp-.*.php|/feed/|index.php|sitemap(_index)?.xml") {
               set $no_cache 1;
       }

        #Don't cache if there is a cookie called PHPSESSID
       if ($http_cookie ~* "comment_author|wordpress_[a-f0-9]+|wp-postpass|wordpress_no_cache|wordpress_logged_in") {
               set $no_cache 1;
       }

        location / {
                try_files $uri $uri/ /index.php$is_args$args;
                # try_files $uri $uri/ /index.html;
                # try_files $uri $uri/ =404;
        }

        location ~ \.php$ {
                fastcgi_split_path_info ^(.+\.php)(/.+)$;
                include snippets/fastcgi-php.conf;
                fastcgi_pass unix:/run/php/php7.0-fpm.sock;
                include fastcgi_params;
                fastcgi_param REQUEST_METHOD $request_method;
                fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
                fastcgi_cache MYAPP;
                fastcgi_cache_valid 200 60m;
                fastcgi_cache_bypass $no_cache;
                fastcgi_no_cache $no_cache;
        }

and this is my multi-site setup

        if (!-e $request_filename) {
                rewrite /wp-admin$ $scheme://$host$uri/ permanent;
                rewrite ^(/[^/]+)?(/wp-.*) $2 last;
                rewrite ^(/[^/]+)?(/.*\.php) $2 last;
        }

@jtittle @hansen
heres my entire server block

fastcgi_cache_path /var/run/cache levels=1:2 keys_zone=MYAPP:100m inactive=60m;
fastcgi_cache_key "$scheme$request_method$host$request_uri";
add_header X-Cache $upstream_cache_status;
fastcgi_ignore_headers Cache-Control Expires Set-Cookie;

    # Expires map
    map $sent_http_content_type $expires {
    default         off;
    text/html       epoch;
    text/css        30d;
    application/javascript  30d;
    ~image/         max;
    font/woff2      max;
    font/woff       max;
    image/x-icon        max;
    application/font-woff2  max;
}

server {
    listen 80 default_server;
    listen [::]:80 default_server;

    expires $expires;

    server_name mydomain.com www.mydomain.com;

    # SSL configuration
    #
    # listen 443 ssl default_server;
    # listen [::]:443 ssl default_server;

    # include snippets/snakeoil.conf;

    root /var/www/html/website;

    # Add index.php to the list if you are using PHP
    index index.php index.html;

    if (!-e $request_filename) {
        rewrite /wp-admin$ $scheme://$host$uri/ permanent;  
        rewrite ^(/[^/]+)?(/wp-.*) $2 last;                     
        rewrite ^(/[^/]+)?(/.*\.php) $2 last;                   
    }

    #Cache everything by default
    set $no_cache 0;

    #Don't cache POST requests
    if ($request_method = POST) {
        set $no_cache 1;
    }

    #Don't cache if the URL contains a query string
    if ($query_string != "") {
        set $no_cache 1;
    }

    #Don't cache the following URLs
    if ($request_uri ~* "/wp-admin/|/xmlrpc.php|wp-.*.php|/feed/|index.php|sitemap(_index)?.xml") {
        set $no_cache 1;
    }

    #Don't cache if there is a cookie called PHPSESSID
    if ($http_cookie ~* "comment_author|wordpress_[a-f0-9]+|wp-postpass|wordpress_no_cache|wordpress_logged_in") {
        set $no_cache 1;
    }

    location / {
        try_files $uri $uri/ /index.php$is_args$args;
        # try_files $uri $uri/ /index.html;
        # try_files $uri $uri/ =404;
    }

    location ~ \.php$ {
        fastcgi_split_path_info ^(.+\.php)(/.+)$;
        include snippets/fastcgi-php.conf;
        fastcgi_pass unix:/run/php/php7.0-fpm.sock;
        include fastcgi_params;
        fastcgi_param REQUEST_METHOD $request_method;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        fastcgi_cache MYAPP;
        fastcgi_cache_valid 200 60m;
        fastcgi_cache_bypass $no_cache;
        fastcgi_no_cache $no_cache;
    }

    location ~ /\.ht {
        deny all;
    }

    location /xmlrpc.php {
        deny all;
    }

    location = /favicon.ico { log_not_found off; access_log off; }
    location = /robots.txt { log_not_found off; access_log off; allow all; }
}

in my php.ini

cgi.fix_pathinfo = 0

i have noticed few other things from https://codex.wordpress.org/Nginx
i installed multi-site and FastCGI according DO tutorials and few things from above link is missing in those tutorials. just want to confirm they are not the reason im facing this problem.

map $uri $blogname{
    ~^(?P<blogpath>/[^/]+/)files/(.*)       $blogpath ;
}

thanks in advance