Ya, two possible causes, the first is most likely the real one:

1. Your non-admin /includes/configure.php file probably doesn't have an https:// URL in the HTTP_SERVER define. Remember it's probably been flipped to be a read-only file as well, so you'll have to make it not-read-only before you can save changes to it.
This file is the central place for all URLs your storefront generates for customer-use. (The admin version of the file is the central place for all admin-related URLs)

2. Your template might not be telling it to actually use SSL (older templates didn't always do that on all forms).
Notice here the use of 'SSL' as one of the parameters: https://github.com/zencart/zencart/b...efault.php#L67