Woocommerce order and inventory management after 4.0 upgrade

I upgraded my blog site to 4.0 and have some problems with my Woocommerce.

1, when I finish my order, the website seems no response and no any sign show me that the order is created. But when I go to dashboard and see the new order is there.

2, Products inventory doesn’t change at all after the order is created.

Is anyone encountering the same issue as this? Or anyone can help me fix this problem? Many thanks