Why is only one of the participants getting a ToDo email notification when an action is assigned to multiple people?
The Assignment method of that action might be set as “Automatic to the person” instead of “Self service”.
When editing the action’s Assignment Method, you can assign an action to a dyamically changing list of multiple users by using the “Retrieve user from” dropdown option and selecting a Process Data that contains a comma separated list of usernames. Using “Automatic to the person” will only pick the first user from the list of users in the process data and only this selected user will receive an email notification.
If you want to assign an action and send out notifications to multiple users as a team, always use “Self service” as the action’s assignment method.