Z axis not cutting to required depth

[JAZZCNC]

I can say that this a sudden occurrence during this particular job

So are you saying it's been working OK then suddenly done this.?

If yes has it just done it without any changes to Mach.? By that I mean not changing any motor tuning settings or any thing.?

Can you post the G-code file so can take a look.

Edit: Can you give following details of machine so we can verify steps per is correct.

Thread pitch or turns per inch along with any ratio if geared.
Drive model and micro stepping set to IE 400,800,1600 etc could show on drives as 1/2 or 1/4 - 1/8 etc or 4X 8X 10X
Confirm steppers are 1.8deg (200 steps per rev)