I know nothing. Less about CNC. Less still about plasma. But I'd slave an LED on the NVUM output to trigger the torch and re-run, re-video a cut with the LED and torch in shot when it completes. If the LED on the NVUM extinguishes at the same time as the torch extinguishes, then the problem is likely one of the NVUM motion controller. The G-Code that you posted indicates no problems - once you get over the lead-in that it adds presumably to generate a clean cut from firing the torch. That the distance uncut lengthens when the feed rate is doubled suggests to my poor addled brain that the motion controller is running ahead of the pulse generation and shutting the tool (torch) off early.

Might be worth experimenting with a G04 instruction before the M05.

e.g. was:

N0680 M05
N0690 G00 Z10.0000
N0700 X0.0000 Y0.0000
N0710 M05 M30
becomes:
N0679 G04 500
N0680 M05
N0690 G00 Z10.0000
N0700 X0.0000 Y0.0000
N0710 M05 M30