There seems to be a limit on how far down you can go.
This makes it a problem to set the Z zero.
I can use the probe most of the time but there are
Times when you need to set it by hand with a piece of paper.
Is it a carbide motion software problem?
You do mean HDZ, not Z-plus, correct?
If you have a wasteboard on top of your baseboard, and the router seated all the way down in its mount, you should be able to go low enough.
Can you post a pic maybe ?
This is how far mine descends above the spoilboard (front steel frame in shot for reference of how little spoilboard is left)
The bottom edge of the moving Z plate (with the spindle) is a couple of mm above the bottom edge of the fixed Z plate (with the V wheels) and around 104mm above my spoilboard.