I would suspect that the very high spindle accel. current is possibly dropping the artificial phase voltage enough to cause a fault to be sensed in the spindle drive, possibly in the third phase in general and this in turn is being sensed by the other parts of the system also.
I believe there were different spindle drives used on the 6 systems, usually DC spindle with analogue control. AFAIK there is no accel. parameters that can be adjusted as there is in the servo's.
You may have to try adjusting the gain control on the spindle drive, or finding other creative ways to accel. the spindle.
For that size of spindle the accel. current can be very high.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.