Even you unselect "Continue selling when out of stock", there still have chance of overselling a connected product.
Connected Inventory requires few seconds to receive order event from Shopify. If customer A just bought the last item, and customer B placed an order of the connected products within few seconds. Oversell will happen.
Due to the fact that the inventory synchronisation to the connected products happens after the order is placed. If the customer put the connected products in the same cart and checkout. Oversell will happen.
For bundle group, the app will calculate and refresh bundle product inventory every 10 minutes. When customer A just brought the last bundle product, and customer B placed an order within that 10 minutes. Oversell will happen.
Because there is a chance of overselling, we suggest reserving a few additional products as buffers. For example, if you have 50 left at your store, reserve 5 of them and input just 45 to Shopify. That will give you 10% buffer to cope with the situation of overselling.