A remote station can disappear from a dashboard while continuing to measure. A logger can store data while a modem is disconnected. One receiving endpoint can fail while another still sees the station.
Loss of visibility is not automatically loss of measurement.
Name the layer
A useful first step is to separate the path: instrument, logger, local storage, modem, network, server, processing and display. “Offline” can occur at any one of those points, and the evidence produced by the others may still be available.
Historical data that returns after communications recover suggests something different from a logger that stopped recording. A station visible to one server but not another suggests something different again.
Why this matters beyond troubleshooting
If missing telemetry is mistaken for missing measurement, the investigation may mobilise the wrong people or describe a data gap inaccurately. If a failed instrument is mistaken for a communications problem, the apparent continuity may be trusted when it should not be.
ATHAR principle: treat each layer of the monitoring path as separate evidence. Ask where the failure is observed before asking what caused it.
Keep the uncertainty honest
The first answer may simply be: the dashboard has not received new data. That is precise, useful and does not claim more than the evidence supports.