This is what @carter.swedal had to say about this problem:
As far as I can tell, the devices are configured correctly by default to report the proper clusters, but not all clusters are being reported as they should.
The office sensor (Iris V3 Motion Sensor) seems to be reporting as expected, and does not have online/offline changes.
The Freezer door sensor (Sonoff contact sensor) does not seem to report the PowerConfiguration or the IASZone clusters. And therefore it is marked offline after about 2.5 hours without communication
The Workbench Motion sensor (Sonoff motion Sensor) does not seem to report the IASZone cluster every 5 min like we configure it to.
I will reach out to our integration testing team to see if this is a known problem with the device models. In the meantime. One thing you could do if this is a large bother, is to configure reporting for the PowerConfiguration cluster to be more frequent (<2 hours). By default we configure PowerConfiguration to report battery percentage every 6 hours, and IASZone to report every 5 minutes; so we are relying on the IASZone attribute reporting to monitor the device is online for these devices.