The correct answer is D - Set up a meeting with the stakeholder to modify the working agreement and ensure future engagement.
Agile values regular collaboration with stakeholders. When a stakeholder becomes disengaged, the first step is to address it through open communication and mutual agreement. Revisiting or modifying the working agreement helps reset expectations and reestablish commitment in a collaborative and respectful way.
From the PMI Agile Practice Guide:
"Agile teams work closely with stakeholders and set expectations through working agreements that are revisited and refined as necessary. These agreements include communication preferences and participation expectations." (PMI Agile Practice Guide, Section 4.2 - Stakeholder Engagement) Mike Griffiths reinforces this:
"Creating and maintaining stakeholder engagement requires ongoing alignment of goals and expectations.
When participation drops, revisit agreements and reset expectations collaboratively." (Mike Griffiths, PMI-ACP Exam Prep Book, Chapter 3 - Stakeholder Engagement) Why the other options fall short:
* A may help short-term but doesn't address the root issue of misalignment or expectation gaps.
* B comes across as directive rather than collaborative.
* C escalates prematurely without attempting resolution directly with the stakeholder.

Explanation/Reference: