I corrected the problem in the checkout where the shipping and payment method sections were not displaying.
The problem was where users were keying in orders as new customers, but they had either ordered from us before or they had already registered their email in the site with intent to order later.
Normally this would not be a problem, but the "Already Registered" error message with log in link was ALSO not displaying. This has now been corrected!
All customers should now be able to checkout normally.