Woocommerce Stock Quantity reducing wrong

Hello,

When a customer orders anything from the store, the stock quantity drops down to negative numbers. There is no pattern as which products will go down to negative numbers – some products do but not always, the quantity can be 1, 12 or even 30 and they drop down to negative. Not every order makes this happen. I am not using variations and all the products have unique IDs.

If anyone can point me to the right direction, that would be helpful, thanks!