Woocommerce orders

I have this problem in my Woocommerce store:

When new Woocommerce order comes in, it reduces the stock twice.

So if customer orders one product, woocommerce reduces two products from the store.

Have you heard about this problem before and do you know how I could solve it?

It was suggested to me that this could happen if the "thank_you" hook gets loaded twice. How can I find out if this happens?

Thanks in advance!