Back in stock notifications not being sent

I have seen others reporting that they are not receiving the email update when a product comes back in stock, I’m having the same issue, picked up the following error in my logs that seems to show every time the dc_start_stock_alert cron hook is run and there are emails to be sent:

PHP Strict Standards: call_user_func_array() expects parameter 1 to be a valid callback, non-static method WOO_Product_Stock_Alert_Action::stock_alert_action() should not be called statically in /home/bedeviousc/domains/fwc.bedevious.co.uk/public_html/wp-includes/plugin.php on line 601

Any ideas what the issue is here?

https://www.ads-software.com/plugins/woocommerce-product-stock-alert/