Shimano walk mode - judder??

[Pinch_flat]

I have a weird issue that I wonder if anyone else has had. I had my motor replaced by Shimano and the walking mode just isn't right as its judder I guess would be the best description, even when lifted off the ground the motor doesn't apply constant smooth power but rather a jerky rotation of the motor.
The old motor wasn't anything like this so I know that there is something wrong with it but I'm wondering if it's due to a software glitch or a mechanical problem
Anyone else had this issue? Did you manage to get it fixed?