Nosram pearl v2 & speed passion v3 sensor problems

[nites]

I need some help or info with my set up as i keep blowing sensor boards in the motor.
My set up is a nosram pearl ISTC version 2 and the motors are both speed passion v3's ( 5.5 turn and 6.5 turn). This is in a kyosho lazer FS1 with 16tooth pinion.
All appears to be working properly but i have just blown a 2nd sensor board in a speed passion v3 motor ( one is 5.5 turn and the other is 6.5 turn). I have now blown one sensor in each motor.
I keep dropping one sector in the motor so that if the motor stops in that sector/segment it will not start again unless i move it one sector/segment and then it runs ok again unless it stops in that sector/segment.
Also, when i run the car at any speed on the stand, the motor seems to stutter like a normal road car would if it was mis-firing, its certainly not smooth running so i wonder if this normal or if it points to a problem with the ESC.

Any help would be greatly appreciated as i want to start racing soon and dont want to have this problem on my first race night plus its expensive at £30 a pop!

Thanks Nites