A key stakeholder complains that recent project communications were incomplete and late, and is beginning to disengage. What should the project manager do?

The project manager should update the communications management plan because it's a proactive and structured approach to address the stakeholder's concerns directly. The plan defines how, when, and by whom project information will be communicated. Revising it ensures that the stakeholder's needs for complete and timely information are formally incorporated and consistently met going forward, thereby restoring engagement. Explaining current communication methods without addressing the underlying issue won't resolve the problem. Sending all information simultaneously might not be tailored to individual stakeholder needs and could lead to information overload. Asking the project sponsor to intervene is a reactive escalation that doesn't address the root cause of the communication breakdown.