The project manager should meet with the entire team to review the ground rules about safe environments, as this is an important aspect of creating a high-performing team and fostering trust and collaboration among team members1. The project manager should also contact the team member who shared the negative details to explain what information can be shared outside the team and what information should be kept confidential, as this is part of managing the team's communication and ensuring ethical behavior2. Contacting the team member's functional manager and inviting them to the next retrospective (option A) may not be appropriate, as it could violate the privacy of the other team member and create more conflict. Meeting with the product owner to talk about the situation (option C) may not be relevant, as the product owner is not directly involved in the issue and may not have the authority or responsibility to resolve it. Meeting with the sponsor to review the situation (option E) may not be necessary, as the sponsor is not directly involved in the issue and may not have the interest or availability to address it. References:
* 1: A Guide to the Project Management Body of Knowledge (PMBOKGuide) - Sixth Edition, Project Management Institute, Inc., 2017, p. 336.
* 2: A Guide to the Project Management Body of Knowledge (PMBOKGuide) - Sixth Edition, Project Management Institute, Inc., 2017, p. 379.