By default format descriptions are hidden on out of stock items. This is to declutter the product page where possible.
It can be shown again by adding some custom CSS.
Site Settings > Design > Custom Styles
.format-unavailable .long-description {
display: block;
}
or to show only for a specific product, add the following CSS (where 000000
is replaced by the product ID you want to hide bundle items on).
#product-000000 .format-unavailable .long-description {
display: block;
}