Shimano E6100 strange problem


New Member
United Kingdom
I have a BMC Alpen challemge AMP bike which has the E6100 motor fitted, had it for two years
It has developed a very strange problem, when I first set of the the handlebar display unit shoots upto 30 mph ish and then drops down to the actual speed

Once pedalling if I put any kind of force into the pedals it does the same and of course the motor cutouts, pedalling lightly in a high gear ( large gear on hub) it appears OK
change to a low gear and it does the same thing

I did notice that sensor on the the rear disc and frame was covered in crud which I have cleaned but not been out on it since

Any ideas/theories before I book into a shimano service centre

Thanks Chris