Question M700 loosing step

Hi,

I have a problem with my M700. I try to describe what it is about. Before that, in order to solve the problem more easily, I am sending all the information about the CNC and the programs I use.

CNC: M700 (purchased in December 2020.)
Milling machine: AMB Milling Motor 1400 FME-P DI
Automatic Tool Changer for AMB with Switch-Box

CNC Software: UCCNC for STEPCRAFT V3.4
CAD/CAM: Vectric VCarve Pro 11

Problem:
I tried to make signs from 3mm alubond. I used 3mm and 1mm for pocketing (0.8 deep). Everything went well and there were no problems. After that I use the same end mills 3mm (Amana Solid Carbide Polishing End Mill 3 mm, O Single Flute for Aluminum, Up-Cut) to cut out the sign. The spindle speed is 22.000 r.p.m. and the feed rate i a litle bit more then the default settings (around 1000 mm/min). Everything works normally (arrival of the spindle at the starting point is according to the settings). At the moment when the spindle starts entering in to the material and when the machine start working the feed rate, according to my estimation, is certainly half the settings I gave it. Milling machine with the x and y axes vibrating .... it seems to me that the machine is losing the step.
I checked all the mechanical parts in particular igus® dryspin threaded lead screws. Everything seems normal to me. The machine is connected to a ground that is not on the same power cableas the mashine.
In the UNCC General settings the step per unit for X, Y and Z axis is 160.
Otherwise ... the machine is very well maintained and regularly lubricated. I keep in my lab.

Has anyone had similar problems?

Thank you in advance.