By default, the app automatically reloads the page to ensure the (drawer) cart content is updated and reflected on your shop. This happens when:
A free gift is added (or removed)
A BOGO line is split into two lines (one discounted and one non-discounted)
Improve the UX
To improve the user experience, you can:
disable the refresh; this can be useful on themes that do not use a drawer cart.
To do this, go to Settings > General > Advanced in the menu of the app:
In the tab "Refresh behavior", click "Override flags" if necessary.
Disable, one or both checkboxes to avoid reloading the page on the cart page or other pages (drawer cart).
Each theme is different, so, unfortunately, we can't provide the exact method you'll need. Your Shopify developer can help you to identify which method to use.