I have a Chevelier lathe with a FAGOR800T control. It is an older control but the lathe runs good. But lately i've noticed when running ISO programs sent in, after the second run of a program its very choppy from line to line. Like the tool pauses then moves, pauses then moves. If i reset the control to start the ISO program or say modify the program and restart the choppy movements are gone.

What could cause this. I havent noticed if it is just Z but i believe it is.