The best approach in this situation is for the project manager to meet with the team members and the developer individually to understand the underlying issues and perspectives. This aligns with the conflict resolution strategies outlined in the PMBOK Guide, which emphasizes the importance of addressing conflicts proactively and collaboratively12. By meeting with the parties involved separately, the project manager can gather unbiased information, which is crucial for formulating an effective action plan. This approach also allows for a more personalized discussion, where each individual can express their concerns without the pressure of group dynamics. Once the project manager has a clear understanding of the conflict's root causes, they can work with the team to develop a resolution strategy that addresses the concerns of all parties and supports the project's goals.
References: The PMBOK Guide and materials on conflict resolution techniques for project management professionals, as well as best practices for business analysts in managing conflicts123.