Correct answer: A missing or improperly seated air baffle/shroud.
Server chassis are designed with precise airflow channels, often managed by plastic air baffles or shrouds. These components direct air from the fans over critical components like the CPU heatsinks and VRMs. If a baffle is missing or improperly seated after maintenance, airflow will not be correctly channeled. Even with fans at full speed, the VRM can overheat due to a lack of directed cooling, leading to a thermal shutdown. Since the CPU and chassis fans are working, a disruption in the engineered airflow path is the most probable cause.