I've received an email from Prey to say that my laptop "hasn’t made contact with the Prey servers for more than a month". I am running Mac High Sierra (10.13.2).
I logged into Prey. There was a message saying "Unable to reach device". My device status was "Unavailable" ("Hasn't connected yet").
I visited my activity log. Apart from a few data requests from the last 3 hours, there was also an event from 15 hours ago saying "[missing "en.events.device_dead" translation]" Perhaps this is related to the issue?
Another possible factor is that I have been occasionally using a VPN over the last month or so. The VPN hasn't always been activated, but perhaps this is related.