Micro stepping not taken into account ?

Is this after a long feed move, or after a rapid move?
How far does the system have to travel to each maximum speed?

What are your following-error limits?

andypugh wrote: Is this after a long feed move, or after a rapid move?
How far does the system have to travel to each maximum speed?

What are your following-error limits?

This is after a very long milling operation (about 80 minutes) on wood...

This operation has 2 parts a rough and a finnish, the rough is at 2m/min and the finnish at 5.4m/min
The rough is slow and seems to be ok it looks like the gap builds up during the finnish phase at high speed

FERROR is set to 1 machine unit so 1mm
After the operation I see about 6mm gap difference with the origin just for the Y axis

The X axis has the same micro stepping setting (16/step), the same FERROR (1), the same max speed (5.4m/s) and does not create gaps at all...

I am now checking the coupling and mechanical potential issues.. but look ok...

... and MIN_FERROR is 0.25mm

Don't ignore the possibility of a mechanical problem, perhaps when the motor gets hot it loosens a coupling. It might be worth marking the alignment with a marker pen.

If you haven't triggered a following error then the system thinks it has sent the steps, so the question becomes why the machine has not responded to the step commands.

Is there any evidence on the part that the problem happens in the same place? Perhaps a ramp in a corner, where the stepper stalls-out.
You might be able to figure out it it happens once per layer, all at once, or imperceptibly slowly.

andypugh wrote: Don't ignore the possibility of a mechanical problem, perhaps when the motor gets hot it loosens a coupling

I believe you were entirely right, this happened only after a lenghthy milling operation and we did tighten even more the couplings and the problem is gone.

Thank you so much for your help and to those like you who did provide support...