This issue usually occurs because the bundle you're trying to view is not Active and published to the Online Store.
Just like any product on your store, the Bundle product needs to be published for users to see.
Is your bundle product Active?
Is your bundle product published to Online Store?
Are you viewing the changes on your live theme, or a preview theme?
Sometimes preview themes can be cached, or a little buggy. Try going to your product link directly:
For example, navigate directly to your product. The url should look similar to this:
https://biscuits-bundles-demo.myshopify.com/products/cupcake-12-pack
The link should not look like this:
https://56mzkn6a9z06fh4f-59994568057.shopifypreview.com/products_preview?preview_key=8d5f2207e5f80240da49956d7335e5a7
If you're still have issues, please reach out to us.