If these kind of incidents aren't optical illusions or equipment malfunctions (two very big if's!) then the next most likely explanation IMHO is that these are

If these kind of incidents aren't optical illusions or equipment malfunctions (two very big if's!) then the next most likely explanation IMHO is that these are drones being used by foreign nations to probe our nation's defenses and/or send a message to us that they have some very advanced unmanned aircraft. If true (big "if!") that would explain why only military pilots have reported these things.