Unlike Single SKU Bundles, the Multiple SKU Bundle type uses Shopify's system of draft orders.
For this reason, their respective checkout pages display slightly differently:
When a Single SKU Bundle is purchased, the customer will see the Continue shopping icon.
When a Multiple SKU Bundle is purchased, the customer will not see the Continue shopping icon.
Single SKU Bundle Confirmations
Having just purchased a Single SKU Bundle, the customer will be able to view the Continue shopping button at the bottom right-hand corner of the screen.
Order confirmation of a Single SKU Bundle.
Multiple SKU Bundle Confirmations
On the contrary, order confirmations of Multiple SKU Bundles will not display the option to Continue shopping.
Order confirmation of a Multiple SKU Bundle.
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Draft Order System
This is because Bundle Builder uses Shopify's system of draft orders as a basis for Multiple SKU Bundles.
Draft orders were designed to be a system for merchants to create orders on behalf of customers - for example, for stores taking orders over the phone, in person, or through external sales channels.
For this reason, the order confirmation page for a draft orders purchase is designed to be seen by the merchant rather than the customer - therefore, the Continue shopping button is not visible.
Unfortunately, as this is a result of the app working around the Shopify platform, the only way to ensure the Continue shopping icon is visible on the order confirmation page is to use a Single SKU Bundle.