Can't proceed to checkout if the dark background framed poster is in the basket/cart

## What Happened
If one of the new framed posters with the **dark** background is in one's basket, it won't proceed to the checkout on Shopify/Shop. Whether it's the sole item, or other items are included doesn't matter; if one of these is in the basket, it won't proceed.
I've tested each 'SKU'/product ID, each representing a combination of the background colour and frame colour choices and it appears to be affecting any of the dark background ones, whichever size or frame colour, whereas the version with the white background seems fine.

For example; if you have a 'Terminal Pillow - 18×18' or 'edw Sticker Sheet', it'll proceed to the Shopify/Shop checkout successfully. However, if you _also_ have the 'Palette Framed Print – Dark - Black / 24×36' framed poster, it won't. I've tested against both U.S. and UK address and that doesn't appear to play a role. I've also tried with disabling all extensions/plugins for each browser (and was part of the reason I eventually tested with Chrome on Android to ensure nothing custom in my desktop browser was the cause of the issue).

I don't see anything appear in my console and after the request with the redirect and POST to Shopify/Shop, there are no clues on the store end but it cleanly finishes and the page reloads with the submitted form details being loaded back into state.

## Expected Behavior

With this product in the basket/cart, it should successfully `POST` the data and redirect to the Shopify/Shop checkout page.

## Steps to Reproduce

1. Go to the store
2. Add the ['Palette Framed Print – Dark - Black / 24×36'](https://store.elementary.io/products/205256971/2312273475), ['Palette Framed Print – Dark - Black / 12x18'](https://store.elementary.io/products/205256971/2312273474), ['Palette Framed Print – Dark - White / 24×36'](https://store.elementary.io/products/205256971/2312273477), or ['Palette Framed Print – Dark - White / 12×18'](https://store.elementary.io/products/205256971/2312273476) to your basket/cart
3. Optionally, add another item that's not one of the affected products, (such as the examples noted under **'What Happened'**)
3. Go to your basket/cart and fill out your contact and address details for shipping
4. Click 'Get Shipping Rates'
5. Selecting an option (in my case, only one of 'Flat Rate') and click 'Checkout'
6. The page should end up reloading with the details for the form being reloaded into state

If you want to confirm the alternative (the process working as it should), repeat this again but with the variant that has the white background.

### Logs

## Platform Information
* Browsers:
* Brave
* Chrome
* Firefox
* Operating Systems:
* Linux
* macOS
* Windows
* Android
* The latest versions of the above (both browsers and OSes) at the time of writing