By default, as of a Soapbox update in August 2016, registration forms display separate First Name and Last Name fields rather than the single full Name field. This is to more accurately create and update Contact records in Salesforce associated with the web user registration. Previously, the value provided in the Full Name was split at the first space to determine first name from last when creating and updating the Contact record in Salesforce. Now, the separate fields more accurately create and update the Contact record in Salesforce.
For sites with overrides of the default registration form, the Full Name field will still be used. This will continue to break the first and last name at the initial space.
If you wish to update your registration form to include separate First Name and Last Name fields, please open a ticket and we'll be happy to assist!