Approval Email notification cannot send out to the members of a group. For diagnosing purposes, in a request detail page, click the "Email" button trying to send a request email to an individual contact or a group (to which this individual contact belongs) to test:
When inputting the contact's userid in "TO" field, CA Service Catalog identifies it as an individual contact, and then it will get the contact's email address from the ca_contact table in the MDB database. However, when inputting the group name in "TO" field, CA Service Catalog identifies it as a group, and then it will query EEM about the membership information of this group and get each member's email address from EEM instead of the ca_contact table here. So, if the contact doesn't have the correct email address also in EEM, CA Service Catalog will not able to get the contact's correct email from EEM and therefore cannot resolve the group name to its member's email address accordingly in "TO" field.
CA Service Catalog 17.1 and higher.
Check and Make sure the contact has the correct email address information in EEM also: Login EEM UI as EiamAdmin, go to Manage Identities -> Users -> search and locate the contact, and make sure it has the correct email address there.