It would seem many here do not understand how an ATS system works . In general erratic behaviors / mode S SSR extreme returns are filtered out . So that could explain why the aircraft was maybe not " visible " but the data is in the system and can be retrieved . It just takes time .
Recordings to be recovered and evaluated also take time and need specialists . Their first action is generally not to call the press . So a bit of patience before going into establishing " facts " and deducting wild theories .