Hi Lacy,
This is happening because you selected the audience of "all users." All users means anyone who has logged in to your Attendee Website or anyone who has downloaded your Event App, regardless of if they logged in or not. So this means that the data tags will not render for those who have not logged into the Attendee Hub as the system will not know who they are. So it would just show the first name and last name data tags if they have not logged in yet.
If you want to keep the audience set to All Users, I would recommend removing the data tags so that they don't show {[C-FIRST NAME]}{[C-LAST NAME]} for those who haven't logged in. Alternatively, you could change the audience to all attendees and that will let you send to everyone and the data tags will render properly.
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Julia Plymack
Senior Customer Success Manager
Cvent
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