Saw some unsubstantiated claims that the planes shot down didn't even have it on

That is the basis for my theory. Not being on

And

Being on but jammed look the same from the perspective of the one shooting them down.

Also, I wonder how resilient it is to the gps spoofing that been going on. If they managed to trick it into identifying itself as a few hundred miles from where it actually was, then very hard to know where it actually is.

All of which is well within Irans technical capabilities.