Weird php in dashboard on product save

I’m getting PHP code showing up on my dashboard after saving a product, for example:
Array ( [action] => Add_Product [_wpnonce] => 62288df380 [_wp_http_referer] => /wp-admin/admin.php?page=UPCP-options [Item_Name] => ... I can handle it, but I can’t let a client see this and freak out.

https://wordpress.org/plugins/ultimate-product-catalogue/