What is the primary concern with Windows sensors going into Reduced Functionality Mode?

The primary concern with Windows RFM is that sensors do not have full visibility into all events occurring on the host. In Windows RFM, the sensor continues operating at reduced capacity and can still report events and trigger detections, but it temporarily unhooks from some kernel elements. Without those kernel elements, some detection patterns and a small number of preventions may not trigger. The host is not necessarily offline, powered off, or unable to communicate with the cloud. RFM is also not the same as an operating system crash; it is a protective compatibility state. The CCFA sensor deployment topic emphasizes that RFM reduces visibility and prevention coverage, which is why administrators should identify and remediate RFM hosts promptly.