The presence sensor is losing connection with the hub. There are actually many different reasons why this can happen, so it’s best to contact support as they can do some diagnostics from their side. Some of the reasons why this can happen:
One) as you mentioned, a faulty sensor, although this is fairly rare
Two) low battery
Three) the hub going off-line. This is one of the things that support can check
Four) local interference from either another zigbee device or from boosted Wi-Fi. This is a problem that can come and go. I have a problem every afternoon shortly after school lets out, which leads me to believe that one of my neighbors has boosted Wi-Fi and a student arriving home is increasing their traffic from a game console or Netflix or something.