Issue:
When a customer adds two (2) of the same event tickets to their cart and proceeds to checkout, they only receive one multi-ticket email.
Solution:
Evey has a feature that allows you to set a threshold for the number of tickets a customer needs to buy to qualify as a "group". In the notifications section, you can set this threshold to any number. If a customer buys that many tickets, they will receive a multi-ticket notification instead of a single-ticket notification.
If you want everyone to receive the same notification, regardless of how many tickets they bought, make sure this setting is disabled.