Hi Denise,
Hope you are well!
I got this checked but I was not able to replicate the issue at my end. I would suggest you to contact our Support team and they can escalate the issue to our Technology Team to investigate on it further.
https://support.cvent.com/s/communityarticle/Cvent-Support-Hours-and-Toll-Free-Numbers
Alternatively, you can add the event title within the email subject manually instead of using a data tag and that might work as well.
I hope this helps. Please let us know if you have any further questions.
------------------------------
Raashi Semwal Khati
Senior Quality Analyst
Cvent
------------------------------