Users are not receiving reminders for some games after being subscribed to the notifications. After looking at the Notification History, it is noticed that the notifications were not sent out.
This can be caused when a game is added without Send Notification being marked. This acts as a trigger for both the Game Added notification as well as the Game Reminder notifications. This would need to be marked when the game is added, as the notification will not be re-triggered if the game is edited and Send Notification is then marked.