Also change P062 to 3 which will show current draw in Amps on the display (instead of motor frequency). This may give you a clue as to what is going on.

On the accel/decel suggestion - my unit was shipped with very low accel and decel rates by default (50 Hz / s) so the current draw should be low when changing speed, although this depends on the inertia of the grinding disc (and motor armature). To test this out you can make this even slower in P034 & P042 (accel / decel) and set it to 25 or 10 Hz / s in case that sorts it out, then go up from there.

If not double check the parameters above for your motor settings . . . .