Sorry, but I’m not following you. The device_tracker entity, like any entity, already has a last_changed field. And it’s already displayed in the frontend, as you show. Also, Life360 device_tracker entities have a last_seen attribute (which is also displayed in the frontend if you click on the entity to see the “more info” dialog), which gives the time that Life360 last updated the member’s details. So I’m not understanding what functionality you would like me to add that isn’t already there.
Regarding the error messages, I’ll play around with the idea. I’ve never really been happy with the general situation of entities flooding the log with the same error over and over, but like I said, that seems to be the norm. Still, I think it would be good if for a given member, if the exact same error message is happening one after another to just show it the first time, and then maybe log an INFO message when the error stops.