I am the author of LiveTraffic, an X-Plane plugin, which can use OpenSky data to display aircraft in the simulator. LiveTraffic uses the REST API. Sitting at KLAX the request will look something like this:
When I was following up on appearing and disappearing objects around KLAX I finally catched responses from OpenSky, which contained the many objects I were looking for. These objects appeared on positions around the apron, often actually on the streets used by airport support vehicles. I am aware that ground vehicles can carry ADS-B equippment and even have logic in LiveTraffic to identify them and display them as follow-me cars.
But the data in question is surprising in that it
contains many such objects (varying, but we talk about up to 108 occurrences in just one single OpenSky response),
for only a brief period of time (like a minute or two),
reappearing, that means when waiting long enough they will come back...I am looking at the data like now (21:00 Zulu), and that is a good time every day, and rarely need to wait for more than 5 minutes, re-querying every 20 seconds,
all fo them carry country "Italy"...that was what finally convinced me to ask here...why Italy???
This is an issue with ADS-R used in the US. It shouldn't happen but there's a single sensor that's causing this, which I'm investigating (setup etc.). I've taken it out for now at least. Thanks for reporting this and whenever you notice something just let us know!