Hi Jarrod,
Here’s a good explanation about the differences between the 2 plans from PMP Jonathan Emmons, albeit from 4 years ago:
Clarification reg-Stakeholder Management Plan
Communications management plan––
Documents the information flow to and from stakeholders as well as information governance and storage.
Some examples in this plan: language, level of detail, frequency, method (email, meeting, etc.), reason, confidentiality, and escalation process
From Jonathan:
“… how the messages are generated, sent, controlled, etc. In other words, this is the mechanical part of the communication.”
Stakeholder engagement plan––
Outlines strategies about the level of involvement and expectations that stakeholders have to maintain their support and minimize resistance of the project.
Some examples in this plan: requirements/expectations gathering, influence analysis, engagement activities
From Jonathan:
“… who needs to be engaged and how we need to go about increasing and/or maintaining their support. This has less to do with the mechanics and protocols and more to do with strategy and tactics.”
I remember having difficulties distinguishing these too, Jarrod.
I wish you best in your PMP exam. Go get 'em!!