WPLMS does not interfere in WooCommerce order process. So, if the orders are not auto-completing then it lies under WooCommerce, mostly it is a settings issue but many times we find that WooCommerce itself fails to mark the order as complete.
If orders are not auto-completing then WooCommerce recommends the following :
- Check if product in order is Virtual and Downloadable
- Check if payment gateway is automatic and does not require manual approval.
In many cases users have resolved this by installing following plugins :
a. Free : https://wordpress.org/plugins/woocommerce-autocomplete-order/
b. Paid : http://www.woothemes.com/products/woocommerce-order-status-control/