According to the Project Management Professional (PMP) principles, when a previously resolved issue reappears and the earlier mitigation strategies are not effective, it is important to reassess the issue. This is part of the monitoring and controlling process group, which involves tracking, reviewing, and regulating the progress to meet the performance objectives defined in the project management plan. The project manager should reassess the issue, possibly identify new risks, and plan new mitigation strategies. References: Project Management Professional (PMP) Certification Handbook, PMBOK Guide (6th Edition), Chapter 4: Project Integration Management, Section 4.6 Monitor and Control Project Work. Professional in Business Analysis (PMI-PBA) Handbook, Chapter 6: Monitoring and Controlling.