According to Greek media (roughly translated by me):
"There was a normal radio call above KEA waypoint between the flight and Athens ACC at approx 0300am LT. The next call was due 20 minutes later, prior to exiting Athens FIR and handoff to Egypt. The plane never responded to repeated ATC calls. The plane was still visible on radar. The plane was then lost from radar approx 7nm after entering the Egyptian FIR just south of KUMBI. Athens asked military radar whether they were tracking the aircraft. They were not. Athens raised SAR and notified Egypt. A C130, a helicopter and an early-warning aircraft were scrambled as well as a frigate (HNS Nikiforos Fokas) following reports from the captain of a merchant vessel that he saw a "flash" in the sky 130nm south of the island of Karpathos."