This is just how Bundler works. It applies bundle discounts by creating a discount codes with discounted items, then redirecting the customer to the checkout and applying the discount code in the checkout
If your bundles are popular, then Bundler will create a new discount code every time it applies the bundle discount. There is nothing to worry about. 

If you don't want the app to apply discounts with discount codes, then you can turn on the feature in Bundler -> Settings -> Discount modes to apply the discounts with draft orders (instead of discount codes).