in the first step, a closed Loop Motor is the same for Mach3/CSlab, because it is only Streaming step and dir signals
to the stepper Controller. only the stepper Controller has control over the closed Loop.so in this case i would search
at stepper Controller side. had also some Trouble with CSLab and Epid error. CSLab recomend to use Mach Version 043.022.
i do not think that the Controller was "adding" step's, this normaly allways means it is loosing steps.
anyhow there is no way to "turn off" this EPid error message on Mach/CSLab side.