Hurco conversion using VSD-XE and Mach

My hardware configuration:
-Drive type: VXD-E, device type 270
-Motor: 2-pole brush, Electri-Craft permanent magnet
-Drive FW: 208
-Mach 3, Three 10A switchmode PSUs

Problems arise when:
We try to run both motors simultaneously, ie cut a circle (in the air). Either X or Y will fail with overcurrent at random. Both are set to PIV and we have fiddled the parameters until we got a nice step response. For testing, we have set the Peak current to 7A, the average to 3A and the fault current to 30A.

Odd detail. We initially had this really weird problem where the Y-axis drive would indicate overcurrent, even if the motor was not running. This happened when we ran the X-axis.

Everything is mounted in a large steel enlosure. The drive PCBs are bolted to SS angles which are bolted to the enclosure. We suspected a ground fault and indeed, that error went away when we made sure that the cards only had ground contact through the wiring.

What additional info should we provide?