Some more observations about this:
Wrt point 1: The device list will sometimes show some of the devices, but will never list all devices. And this is very random.
Wrt point 3: I’ve isolated the ‘lost GPS’ alarm down to being caused by some strange interaction between the iKommunicate and my Simrad GS25 sensor (GPS + compass). If I disconnect or disable either of these devices from the N2K network the alarms cease. Also, my previous comment about the alarms stopping after a short time was wrong; the alarm condition may stop for a short time, but will then continue after an indeterminate period.
Wrt to point 3, I have a Garmin GMI10 also connected to the N2K network and it also complains about losing the GPS signal. These alarms continue for a short time after power up, and then it seems to settle. If I keep the iKommunicate powered down, the alarms don’t occur.