seems when you choose like 300 products in a category for example ( select all) and choose export
goes back to main cat with php error logs of :
Jan 3 09:43:37 development httpd: PHP Warning: Unknown: Input variables exceeded 1000. To increase the limit change max_input_vars in php.ini. in Unknown on line 0
so add variable
max_input_vars=10000 in the /etc/php.ini