If you have a test lab and want to hit your DUT (device under test) with 3,050 amps at 6,100 V, or melt your circuits with a RF pulse of 3,000 V/M at 6 GHz, I'm the guy you call. It really doesn't matter what the impedance is to me, I can test anything electronic in a car to destruction.
I like the practicality of hall sensors, but every one has multiple coils that can act like antennas. Most of the time RF or magnetic pulses will cancel due to the design, I have seen some go into saturation due to excessive magnetic fields. If you had two hall sensors and a strong external RF or magnetic field, it might be possible to have them both output the same error. The OP did not notice anything that I would look for that might have created this situation. All of the complete cables and electronics used in all cars are tested in an Anechoic chamber for RF susceptibility and for conducted immunity to find and fix these issues before they hit the market. I don't have any reason to question the results of these tests, nor any reason to disbelieve the OP. I've come to believe: in the world of electronics, never rule anything out.