SYMPTOM:
When creating subscriptions on Strategy Analytic Developer, users are unable to add contacts or contact groups into recipients list. Only users and user groups are allowed to add, as shown below.

CAUSE:
There is no need to add contacts/contact groups as recipients, because it is user/user group that uses Mobile, Cache update or History list subscriptions.
A contact is a Strategy object that represents a delivery address (an email address, a file storage location on a network, or a network printer path), so users are able to add contacts/contact groups into recipients list when editing email subscription or file subscription, as shown below.

Both email and file subscription editors are available on Web, not Developer
ACTION:
Add users/user groups into recipients list when editing Mobile, Cache update or History list subscriptions on Developer.