Happened to a few bikes, panel replaced at first service. On some bike this made the panel die completely. Those panels are probably not fully waterproof, air inside expand and escapes when hot, and then fresh air is pulled from the outside when temp is cooling. This fresh air condenses, creating the fog.

As I write this (April 2020) KTM has stopped replacing the faulty panels, there is an announced new model to replace it, dealers have been told to stop replacing them and to wait for the new part instead.