Back In Stock Only Working On Some Items - Shopify

Hi! I’m trying to get Back In Stock set up on my Shopify store and am running into some issues. The button works properly and will subscribe someone to marketing if they check the box, but on some items it doesn’t add the “Subscribed to Back In Stock” action within Klaviyo. Some items it will work perfectly, some it only allows marketing subscription. The products in question have the exact same default product template applied.

I have another Shopify store that is the exact same theme and products (US vs. Canada stores), and I was able to get Back in Stock working perfectly on the US store. Any ideas as to what could be going wrong?

Thanks!