Unable to add second item to cart when using Kickflip product customizer and Digital theme

Hi,
We are having some issues the Digital theme in connection with an app for product customization. The app in question is called Kickflip (https://apps.shopify.com/mycustomizer-1).

Customers are unable to add a customized product to the cart if there is something in the cart already. The add to cart button loads forever when adding the second item. Normal/non-customizable products work as expected.

You can reproduce the issue by going to https://www.dkori.com/products/dkori-custom-design and clicking “add to cart”. Repeat that a second time to see the problem.

I have tried the app with the default Dawn theme, and that works as expected, so I believe that an incompatibility with theme code is the culprit. The theme developers were unable to help out, though.

I have checked the console output on the page with the problem, but I don’t see any relevant logs there.

The only place I can see a difference is in the network logs, where the call to POST https://www.dkori.com/apps/kickflip/products/variants is never made the second time.

I’m out of ideas right now, so any help is appreciated here.

Thank you!