Openbuilds Control seems to pause

I've searched the forums on this and have found a lot of question regarding the Blackbox/control software seemingly pausing when running a job. Most sound like the job physically stops.
In my case I've been running a simple job of milling holes in my wasteboard for threaded inserts or pins and I find the CNC's movements to be erratic. It finishes the jobs just fine but while milling the holes it appears to pause for a split second and then continues on.
I watch the line of Gcode as it does this and you can see the screen stop for a milisecond and then continue on.
No codes, no alarms. Everything says the code was run okay but the pausing just makes the machine look jerky.

My machine setup is a 1000mm x 1000mm New Carve Ultimate kit from CNC4N. I run a 2.2kw water cooled spindle, Openbuilds limit switches, Blackbox controller, NEMA 23 425oz stepper motors.

I had issues originally with the limit switches and USB cable providing a DC ground through the machine but have resolved that issue.

VFD is wired correctly and is ground both at the spindle end and VFD end using 16/4 double shielding control cable.

PC is in good working order but it is old. Running Windows 7. But it exceeds all of the specs required to run the software.

Only seems to happen when running a Gcode file through the control software. I can manually run the machine with the spindle on (say to flatten my wasteboard) and it works just fine.

Any thoughts?

Thanks,

Andrew