When i try to export some data I have a blank screen

If you have a blank screen when triying to export data it’s because your server doesn't have enough memory to handle the data.
To fix it, you should try the following :

1/ Increase the amount of memory that WordPress can use.

Just add this line to your wp_config.php file to do so (just after the WP_DEBUG line) :

define( 'WP_MAX_MEMORY_LIMIT', '512M' );

2/ Slice your export in smaller piece of data using the date filter. Starting by month, then trimester etc...