In both 1.5 and 2.0, there have been numerous times when some aircraft are not visible by other players. When flying the A10C, those "invisible" aircraft are often not visible on the TAD either. On occasion, the pilot of the "invisible" aircraft is taxiing behind me but, when I check F2 he appears to be airborne. I'm guessing it's some type of sync issue. This has happened on different servers and numbers/types of aircraft. There are no players with unusually high pings, etc.