Just had this on a Storefront API store we manage, the app has been live ~2 years.
Disabling password protection worked in this scenario too!
Spent 3 hours explaining to a live chat agent that I did not need a Shopify Expert and this was a Shopify issue only Shopify can fix! Why is support for trying to get anything Storefront related fixed so painful???
As far as I know it started happening on yesterday for the first time for myself and store owners.
God knows how many orders have been lost to this, may have been happening for customers sporadically for months for all I know.
As an update, I do have a support ticket open with the Shopify technical team about this, hopefully they can resolve this!