Z not touching off from Gcode file

HI All, I am just experiencing this issue on a Sheetcam job where the Z axis doesn’t lower to the workpiece, it just stays at its current height then raises to pierce and lowers to cut as if it had touched off.
I have ran a different file through Sheetcam and the problem isn’t there. The only main difference is this file is a single open line cut that basically skirts the outer limit of the droid by about 20-40mm (a half round 1140x470 with edge start/stop), no offset, no leads.
I just recently updated to latest firmware and initially thought it was a bug, but other files are not affected.
Also, it isnt the plasma lead snag either, other files touch off in the same area fine. Has anyone elso experienced this? I’ll upload the file when the forum permits.

Not the fault of the Gcode, this is a known foible of AD - when touching off at the extremities sometimes the bowden cable doesn’t move as easy as it does in close up working. ie the spring sled does not slide down the rails as it should - you can try lubing the rails or helping it down manually.