Summary discussion from Congressional hearings,
Claims are: they don't emit an RF signal, they go dark when anything approaches them, they stay up for 5-7 hours. Several sources claim Iran is behind it.
The White House disclaimed the Iran connection. Others have accused China, while still others accuse Russia. At this point, nobody seems to know. If they do know, they aren't saying.
On two different occasions this year, the latest being last week, Chinese nationals were arrested for flying drones over sensitive sites, the earlier one being a ship building yard on the east coast and the latest one being Vandenberg AFB.
These drone incursions are different, though. In a hearing before NJ's state legislature, the FBI again stated that they do not know from where they are coming, where they are going, nor who is controlling them, but they are investigating.
Also, a NJ public official stated (in the same hearing if I remember correctly) that he himself, along with a law enforcement officer, saw a fleet of drones, estimated to number around 50, coming in off the ocean. He did not see a ship from where they launched. There has been speculation that perhaps the drones were launched from a ship or submarine that was over the horizon.
But, who knows. Once again the U.S. federal government is keeping this entire subject surrounded in mystery, either intentionally or unintentionally.