Im about 18 months into upgrading Mach 3 to 4 with an ESS. If I try to stop a cycle mid operation, the machine wont just halt what it is doing, it will lose position. Mostly noticeable in my Z axis, I will see it jerk and move about 5mm. I found a checkbox that I cant remember exactly what it was, something like "stop" was planned or something.

Regardless that did not fix my problem. I had this issue with another totally unrelated machine that if the e stop was hit it would haze out the PLC and the issue was an earth.

But this one, I tried to stop a cycle yesterday and it actually caused the part to be ruined. So here I am. Anyone have an idea or had this one happen?

Also - whilst I am in the mood. Do you guys shield and earth your stepper motor power conductors?

I always suggest using the Feed Hold before Stop
It is a controlled slow to stop

yes.. if you are not closed loop at the controller, a STOP, Estop, etc. will lose position. That is because you will immediately lose the buffers between Mach4 and whatever controller you are using. I actually changed my screen so that a STOP is actually a feed hold. In addition I have changed when Mach4 loses home and if they click the ENABLE, STOP, press the ESTOP or otherwise stop the machine, they will lose Home and the Mach4 will not start the program.

And all the operators know that if they stop the machine they must re HOME.

Its sometimes a pain, but its a short cycle and the rehoming is fairly quick. There usually is no reason to stop the machine during the cycle in any case.