Not every change needs to be made. Before you make any change, you always need to evaluate its impact on the triple constraint - time, cost and scope - and how those changes will affect the quality of the deliverables. Until you analyze that impact, there's no way to know whether or not it makes sense to make the change.

Section: Monitoring and Controlling

The initial step for a project manager noticing a change in a team member's performance and behavior is to have a private discussion with the individual. This approach allows for an open and confidential dialogue where the team member can share any personal or professional issues that may be affecting their performance.
It is important to address such matters sensitively and without making assumptions. The project manager should aim to understand the root cause of the behavior and performance drop, which could range from personal issues to work-related stress or misunderstandings within the team1.
References: The approach aligns with the PMBOK Guide's emphasis on project managers being proactive in identifying and addressing team performance issues. It also reflects the principles of good leadership and management, where direct communication with team members is key to resolving conflicts and maintaining a healthy team dynamic1. Additionally, the Professional in Business Analysis materials advocate for addressing team conflicts through direct communication to understand the underlying issues and work towards a resolution2.