we have an issue where stock does not go to 0, so if a customer buys something E.g. that has 1 left, the stock does not go to 0. The same happens if there are 5 left and the customer buys 5 it does not go to 0, it stays at 5. And the other thing is that when we cancel the order the qty goes up of the same value, E.g. if the customer buys 2 when it is only 2 left the stock stays at 2, and if we cancel the order the QTY goes up to 4.
We have disabled MSI so this is not related to saleable qty. We had this issue with Magento 2.3.6 but we found out that the problem was related to the payment module we used. We do not use that anymore and the new payment module developer team is saying the problem is not related to their module but Magento.
Hope someone had the same issue.