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 Bundles at the Checkout
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.
Multiple SKU Bundle at the Checkout
On the contrary, order confirmations of Multiple SKU Bundles will not display the option to Continue shopping.
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.