In my case, the devices that go offline are always query for Refresh too often, almost every minute:
Here are the details from some of them:
Guest Bathroom: 8:12 pm, 8:10pm, 8:07pm, 8:07pm, 8:06pm, 8:06 pm, 8:05pm, 8:03 pm, 8:00pm, 7:55 pm, 7:55 pm
Kitchen Sensor: 8:12 pm, 8:10pm, 8:07pm, 8:07pm, 8:06pm, 8:06 pm, 8:05pm, 8:03pm, 8:00pm, 7:55 pm, 7:55 pm
And the same for any other device that is offline and used as temp sensor in ecobeeSetZoneWithSchedule