برای رفع این خطا میشه این کد رو به انتهای فانکشن اضافه کرد
https://stackoverflow.com/questions/38693992/notice-ob-end-flush-failed-to-send-buffer-of-zlib-output-compression-1-in
/**
* Proper ob_end_flush() for all levels
*
* This replaces the WordPress `wp_ob_end_flush_all()` function
* with a replacement that doesn't cause PHP notices.
*/
remove_action( 'shutdown', 'wp_ob_end_flush_all', 1 );
add_action( 'shutdown', function() {
while ( @ob_end_flush() );
} );