Back in stock-button shows 'randomly'

I just setup the “Back in stock” following the guides.

It seems to work very randomly.

Examples below - remember do change to Danish language as it is not setup in English!
 

I hope anyone has a suggestion on what could have gone wrong. I installed the snippet in the theme file (though only on product pages) - and I followed the guide to the point (I think).

When looking at the products below - sometimes the Giv mig besked (notify me) button is shown - sometimes not. Sometimes I have to reload 5-10 times, then it show, then it’s gone.

I can’t see any pattern.

This a product with no variants (but sold out ATM):
https://puretime.dk/collections/knager-i-trae/products/hjort-knage-i-morkt-trae-messing-maengderabat?variant=41825304215748

This a product with a sold out variant (60 cm buet):

https://puretime.dk/collections/svaevehylder-i-trae/products/strangways-svaevehylde-i-trae-med-rund-kant-mork-3-storrelser?variant=41667807969476

I also tried inserting the <a> to force the button to show - but that didn’t work either.