Why is my device offline?

A device is online if we've seen a message from it in the last 90 seconds. Common causes of an unexpected offline state:

• The device (or its gateway) lost network or power.
• The publish interval is longer than 90 s — increase reporting frequency.
• The gateway went offline, which marks all its child devices offline (LWT cascade).

Online status lives in memory, not the database, so it resets if our cache is flushed — devices re-appear as soon as they publish again. See device shows offline for a full checklist.