DRV8711: A&B PreDriver faults only with pulse to pin10 STEP, SPI step OK

Am spinning up 10A Stepper Motor Controller using IRF4110 Fets that have a substantial Qg 150nC and total gate Capacitance of 9620pF.  I have 47 Ohm gate resistors on the low side FETs.  

When I step the driver via software by writing 1 to bit 2 CTRL register all works fine.  If I pulse pin 10 STEP then ... .boom Both A and B side predriver fault and lockout on the first pulse.  Design is currently testing at 20Vm, final design will run at 48Vm.

Also registers are as follows

ctrl     = 0xE00; 
torq   = 0x15D; 
off     = 0x064;
blank = 0x032; 
decay = 0x110; 
stall    = 0x040;
drive   = 0xFF9;

I am at a loss to understand why SPI commanded steps work fine, and hardware pulse command trips PDF.  Pulse input is opto isolated.

All the best,

Dave