The strikethrough price might not appear on the product, even for a single MoonBundle offer.
To fix this, you just need to enable an option in your Shopify settings:
➡️ Go to Markets > International
➡️ Then go to Compare-at-price
Make sure the option “Hide compare-at prices for customers in the European Economic Area (EEA)” is disabled.
Save your settings, then check the product page again.