Loss of supervision indicates that the panel is not regularly receiving the “check in” supervision signal from a sensor or sensors in their allotted supervision schedule. Supervision checks happen roughly every hour, depending on the sensor.
Often enough, loss of supervision may correspond to borderline low battery status, which is most likely the culprit if nothing else has changed.
If a sensor is reporting loss of supervision, the panel will specify the zone. Try replacing the batteries in that sensor first if it has been a while since they were replaced and the sensor signal is not impeded by metal surface or excess distance.