What’s the typical signal strength and signal quality from devices prior to them going offline?
If you take a device that went offline, does it come back online with a power cycle (assuming you can find someone to access it)?
If you take a device that went offline to a physical different area does it go online?
Do you have a hardware watchdog or external watchdog power cycle the device due to not being able to connect?
Is this battery operated or mains power?