Salute!
I can join the conspiracy folks now, and as Wolfie states, they are "supposed to disappear" from radar.
You can see the training "blisters" that are attached on top and bottom near the vertical stabs, They allow for decent radar signatures, but I am not ure if they electronically enhance returns or act completely passively. I suspect they are active and the pilot can turn the things off. Sure, even if passive you might have an RCS the size of a crow versus a hummingbird, but still real hard to detect and track.
So my conspiracy group hypothesizes it could be a defection to some foreign power. That plane has amazing legs with only internal fuel. so let the myths begin!
Gums sends...