When faced with customer dissatisfaction, especially when no specific reasons are provided, it is important for the project manager to engage in a dialogue to understand the underlying concerns. Talking to the customer and the project team member separately allows the project manager to gather information from both sides, assess the situation, and determine the appropriate next steps. This approach is in line with the PMI's guidelines on stakeholder engagement and conflict resolution, which emphasize the importance of communication and problem-solving in project management. It ensures that decisions are made based on a thorough understanding of the situation rather than a hasty reaction.
: (Project Management Institute. (2021). A Guide to the Project Management Body of Knowledge (PMBOK Guide) - Seventh Edition and Standards. Project Management Institute.)