When a key stakeholder expresses dissatisfaction with the deliverables, despite formal acceptance of the quality specifications, the project manager should review the requirements traceability matrix and conduct inspections. This allows for a detailed examination of whether the deliverables meet the agreed-upon quality standards and to identify any discrepancies. The requirements traceability matrix is a tool that links requirements throughout the project lifecycle, ensuring that they are addressed in the final deliverables. Conducting inspections is a method of quality control that helps to verify that the product meets the requirements and standards1.
Reference:
Discussions on PMP exam topics related to stakeholder dissatisfaction and quality control measures1.
PMI's A Guide to the Project Management Body of Knowledge (PMBOK Guide)2.
Professional in Business Analysis Reference Materials from PMI2.

When stakeholders express concerns about poor communication, it's important for the project manager to investigate the underlying causes of the communication issues. Performing a root cause analysis (RCA) can help identify not just superficial problems, but also systemic issues that may be affecting communication. This approach aligns with PMI's emphasis on continuous improvement and problem-solving within project management processes.
PMI's PMBOK Guide and the standards for project communication management emphasize the importance of effective communication and the need for project managers to adapt their communication plans to meet the needs of stakeholders. The PMBOK Guide provides guidelines on how to manage project communications effectively, which includes monitoring and controlling communications throughout the project life cycle to ensure that stakeholder needs are met.
Please note that this response is based on general project management principles and does not reference specific documents or materials. For detailed information, you should refer to the latest editions of PMI's PMBOK Guide and other official PMI publications.

Agile project delivery is adopted primarily because it allows for early and incremental delivery of value, which is prioritized based on customer and project needs. This approach enables teams to deliver parts of the project as they are completed, allowing for early benefits and the ability to adapt to changes quickly. Agile emphasizes customer collaboration and responsive planning which is more conducive to delivering a product that better meets user needs and has a higher value early in the process123.
Reference:
Agile project management and the PMBOK guide1.
Agile and PMBOK guide project management techniques2.
Tips for Adopting Agile Approaches3.