I went thru everything to get my new magnet less speed sensor working. Changed 3 batteries, and now found this post which talked about the fact that the new sensor works based on the earths magnetic field.
Re tested with the bike mounted on a trainer, and the rear wheel free to spin like in coasting, and everything is fine when the left crank arm is facing forwards, while the speed shows zero when the left crank arm is backwards and towards the rear hub. Realised that I had used a rare earth magnet on my crank for a year with my old sensor, so I guess that crank arm is magnetised.
Any solution?