Hi Andy,
The variable recepient_name is injected in the email templates at runtime. In the external user registration email notification, there's also a variable named auth_key which makes the registration URL unique for tha particular user (and is used to pull user details when clicked). Above two variables are populated together.
In the problem you mentioned, if the URL you get in mail is correct I see no possibility of recepient_name not getting populated.
Since this thread is about 4 months old, are you still facing this issue? If yes, please revert with server logs.
Thanks,
Ankit Narang
LiveCycle SA Team