Meeting booked - Issues with confirmation email

When the user book a meeting, some will received a confirmation email but other won’t received this email.
The email is automatically generated by Brevo, but when I look in the log, for both users (the one who receive and the one who doesn’t receive) there is no trace of the email.
both users users have a gmail account and will receive other emails sent with Brevo.
The issue seems to be with the confirmation email for a meeting only.
Does someone know what is happening?

Hi Guillaume, that’s weird indeed.
Maybe @Jonas you know what could happen here?