All of my items in my cart were being shipped to the Storefront. Some of the items were available at the store and some were not (website stated estimated delivery time).
Everytime I went to checkout the website would say, "We're having temporary difficulties arriving at the destination you requested."
After about 15 minutes of retrying to checkout, I decided to delete all the items that were available in the store. What would you know, it worked, the website immediately went to the checkout area.
This could possibly mean there is some errors/glitches in the written code that does not allow the buyer to continue with a mixed shopping cart. Hopefully this solution works for the rest of you.