You can set Fast Bundle discounts to be combinable with other Shopify discounts.
In the Fast Bundle admin navigate to > Settings > Bundle settings > Discount > Discount combination and enable it.
Fast Bundle Discounts are still combinable
It's possible that you turned off discount combination but discounts still get combined with your Shopify discounts.
Most of the time, it's because of the method that is used to apply the Fast Bundle discounts.
Fast Bundle Has Two methods for Showing the Discount
Fast Bundle uses two methods for showing the discount:
1) Discount on Cookie
A unique discount code is generated for each customer session including bundle purchases. This code is stored as a product discount in your list of Shopify discounts and is saved in cookies for display during checkout.
2) Shopify Function Discount
An automated discount that utilizes Shopify functions to implement the bundle discount.
You can read more about the difference between these two methods in this article:
Bundle Discount is Always Combinable in the Shopify function Discount method.
When the Fast Bundle discounts are being applied using the "Shopify function discount" method, the discount combination can't be turned off and Fast Bundle discounts get combined with other combinable Shopify discounts.
We are currently working on allowing the option to turn off the discount combination in the Shopify function method as part of our development program. However, this feature is not yet ready
Contact Support to change the method of discount
If you want to change the discount method to Cookies, please contact support, and we will assist you with this transition.