Thanks for reaching out about this issue. That is definitely a unique problem to have. I'll recommend a few things to confirm and then you will want to reach out to our live support for additional troubleshooting help.
Is your payment options active and without errors?
Do you have shipping rates setup for your store?
Are you using the Shopify checkout flow, or redirecting to a checkout powered by a third party?
Once you have confirmed that information I would then recommend connecting with our live support for additional troubleshooting. To contact our live support please follow this link: Shopify Help Center - Contact Support, sign into your store account, search for your issue and use the contact support button at the bottom of the search results to see all our live support options.
Shay | Social Care @ Shopify - Was my reply helpful? Click Like to let me know! - Was your question answered? Mark it as an Accepted Solution - To learn more visit the Shopify Help Center or the Shopify Blog