Order Status didn’t change automatically

I installed this plugin for nearly 1 year, it works well until recently. Once customer buy the products and paid but the status didn’t change to completed from pending payment automatically. At first, I thought it was an accident, but later the same thing happened again, so I was wondering what is causing this issue? Is it because of compatibility issue or what ever other causes?

WP Version: 5.2.4
WooCommerce: 3.7.1