In that case it's almost definitely the max_input_vars is set to a lower value than the default 3000.
Since with nginx you don't have a .htaccess file, you will have to look for that in the active php.ini file. If it's not in there, just put this line there:
max_input_vars = 3000
Then restart nginx and php-fpm or mod-php or whichever one you are using and it should start working.Best,
If you like my products, don't forget to rate them on codecanyon :)