You have a closing } for the plugin::check_handin(), but if that's the entire file, then you're missing the } for the end of EVENT_ITEM.
Otherwise, I can only guess there's something interfering with your perl. I created dummy copies of your custom items for turning in, and tested with a full replacement of my felwithea\Exterminator_Valern.pl file, after removing the line break and adding the finishing } at the end of the file.
https://youtu.be/U0ZG18wQS_4