event submission not working

Have you changed your hosting recently?

That sounds like a PHP sessions issues.

Please write back with WP Admin and FTP credentials in a private reply and we can check it out.

For temporary fix you can try adding the following lines in wp-config.php file.

/* PHP SESSION TEMPORARY FIX */
if ( !defined( 'GEODIR_USE_PHP_SESSIONS' ) ) {
   define( 'GEODIR_USE_PHP_SESSIONS', false );
}
if ( !defined( 'WPINV_USE_PHP_SESSIONS' ) ) {
   define( 'WPINV_USE_PHP_SESSIONS', false );
}
/* PHP SESSION TEMPORARY FIX */

Are there any other notes about how to recreate the issue?