This is a problem on at least v.5.43. There is a bug in the confirmation email code when adding attendees. The event name will sometimes not be correct it affects the confirmation email sent to the registrant and registrar both.
The issue is in file event_register_attendees.inc.php in the function register_attendees at line 821 and manually_add_attendees_to_db at line 1050:
$event_name = $current_event;
At that point in the code the variable value $current_event is used to build the email message and is taken from the wp_options table and not the events_detail_table.
The issue is one of timing when multiple people are registering for different events at the same time -or- someone is registering for an event while an admin is modifying a different event both of which update the value for current_event on the wp_options table. Commenting out the lines corrects the problem.
The code is significantly different in version 6 and does not appear to be using the wp_options table to store transaction transient based values.
Hope this helps someone - it has been a head scratcher for me.