MurphyWasRight Indeed with GNSS signals what matters is the signal path between transmitter and receiver and any path delays induced by hot air pockets (doesn't have to be absolute temperature hot, but the gradient between the cold and hot air regions). This can modify the refractivity index of the air to a sufficient degree so that arrival times of GNSS signals are sufficiently out of phase that signal lock is lost, and the receivers determine that no reliable position can be inferred, hence showing no position (rather than an erroneous one). All part of GNSS fail safe mechanisms.