Hi Luciano and
to the forum.
I have not come across this particular problem before, but from your description it sounds like the battery power is somehow cutting out under load and immediately cutting back in again.
Which battery do you have, and can it supply enough current for the Magic Pie Edge under full load on it's default setting
(at least 21 Amps continuous)?
I suggest that you carefully check all wiring connections
(especially the battery wires and the battery connector contacts) and make sure that no wires are being pulled
(or the battery pack moving about) when the motor is under load.
Check that the axle nuts are nice and tight
(there should not be any movement between the axle and the fork dropouts).
If you able to video the fault and upload it to YouTube etc. and post a link, it would be very helpful if we could see
(and also hear) exactly what is happening under load?
Alan