Device.cloud.connection.error with a negative value? (-220)

Hi All, I'm encountering a few devices that are having intermittent cloud disconnects - when looking into the connection documents for each device, I can see that they have device.cloud.connection.error with a negative value (-220). Based on the documentation here (comm.protocol errors - Debugging | Reference | Particle), I would expect all errors here to be positive values.
As a note, these argons are connected via ethernet (as opposed to wifi).

On a side note, it seems that the health check mentioned here (Device vitals | Getting Started | Particle) is not present for devices connected via ethernet?
Thanks,
James

Negative values are system errors, just a little below on the page you linked to. However -220 is SYSTEM_ERROR_IO and that's pretty generic.

You should get device health metrics over Ethernet, though obviously the fields related to cellular won't be there.

The best way to troubleshoot is to add this to your firmware as a global, not in a function:

SerialLogHandler logHandler(LOG_LEVEL_TRACE);

and monitor the USB serial debug output and see if there's anything interesting.