Why is a "Back to cart" link missing on my checkout page when there is a bundle discount applied?
When the customer qualifies for the bundle discount, our Bundler app creates a draft order with the applied discount and redirects the customer to the checkout. The back button is not present on Draft Order checkouts because Shopify does not display the back button there. Shopify only displays the back button on normal checkouts.
The only way to resolve this is to turn on the option in Bundler -> Settings -> Discount modes, to apply bundle discounts with discount codes instead of draft orders.