At first, the problem appeared only when a client closed the paypal window, i asked for help, and nicolas recommend this:
There are two solutions in HikaShop to help you here:
1. You use the "order auto cancel" plugin (you need to setup the cron task of the configuration for that) in order to cancel automatically orders after X hours without payment.
2. You remove the stock only when the order is confirmed, and not when the order is created. You can toggle the option "Update the product stock on confirmed status" of the configuration for that.
I already had the 2 option implemented and still had the problem, so, i did number 1. And now, the stock is removed always when the client goes to paypal, even when the client click on "cancel and return".
Thank you so much for your help, my client have some unique products that can be sold only 4 times and some of them, just once, so, i need to solve this.