Not all the observations are explainable. However, if you take away one observation -- the claims about high-g acceleration and supersonic flight -- the following seems to fit: battery powered drones with regular (possibly quad) rotors, sea-launched (possibly from vessels disguised as merchant vessels) by a foreign power to observe US military.

This would explain: FLIR footage and close range radar, but no contact on long range radar. Would also explain why primarily Navy pilots have observed these objects while commercial pilots don't, and why they seem to be seldom seen over land. Also explains why all the sightings seem to be around the continental US. Also explains the lack of exhaust plumes. Also explains the lack of sonic booms (I know of no way a solid object could cross the sound barrier without a boom). Multiple such drones might also explain why they appear to travel faster than the fighters -- perhaps they are observing two identical craft.

All one has to do is discount the high-g claims as embellishment by pilots. I could be wrong, but I know of no way to account for all the observations.