Why is my website showing 'Shipping Not Available' at checkout?

[PK18]

For the past 8 days or so, I've had several customers message me, call, email, etc. that they cannot check out on our website because my website is saying, "Shipping Not Available." 

For example, I had a customer who purchased something, returned it --> We issued her a gift card. 

She went on our site selected what she wanted, then when she wanted to check out, it was saying that we could not ship to her address. It was the exact same address as where we shipped to her initially. 

I called Shopify retail support and upon looking into it, they said they couldn't find any issues because my shipping rules were not address specific or weight specific. They were simply price specific. 

This has started since we switched over to the 1 page checkout.

The exact message is: 

Shipping not available 

Your order cannot be shipped to the selected address. Enter a different address.

Please help! This is affecting our online sales pretty badly. 

[MikeysMerch]

I am facing this same problem.