error in the subject of the email, name of the first registrant and not of the one who has register

As you can see in the screenshot, I am a Booking administrator and I receive an email when someone registers for a service.

For a particular service, when a participant is added I receive an email with an error in the subject: it is the name of the first person who registered that appears in the subject of the email and not that of the participant, can you help me please