Avid XY Loosing steps

Hope I can get some help figuring out this random loss of steps on an Avid 5x10 Mach4.

The problem initially appeared with an run that contained a series of recessed concentric circles, cut at different depths. The diameters, meant to be concentric, were not. The fault occurs randomly, sometimes 3 out of 4 of the exact same feature repeated in the same run is ok, other times one or more would be f’d.

Frustratingly, this problem showed up in the big run of the day in 30mm ply. First run of this file went fine, the second identical file, ran immediately after, was all over the place. See photo…