Why does changing product variants cause a CORS error in the Dawn theme?

[amadeakimmins]

On a fresh dawn theme when changing product variants the "pickup-availability" section fails to re-render due to CORS headers not being present on the response. 

It works when you initially land and click 'Add to Cart' but if you change the variant it causes an error. These are the errors that I get:

 

I haven't changed anything in this part of the theme so am unsure why this has started happening.

Any help on why this might be happening would be greatly appreciated, thank you!