Unexpected Z Axis movement

[TIAEngineering]

Hi Folks,

I own 3 x Next Wave CNC machines. There are two early, smaller Piranhas and I have 1 x XL120 which is the machine in question here.
I use the PC software to run two of the machines and I machine aluminum pretty much exclusively on my stuff.

Yesterday, I created a Virtual Zero file for a recess on a piece of aluminum. I do this regularly, so it is no big deal and I have experience with it. I use metric measurements and after picking up the 8 or so data points that I entered, ran the code. The variations in height measured on the surface were no more than .2 of a millimeter at max, anywhere within the area. I was making light cuts with an end mill of only .1 of a millimeter so taking it very easy on the piece.

The file began to run, and everything looked (and sounded) great. The cut was a rastor, so I was watching it head from left to right. On about the third pass of the initial layer, the Z drop by a mm or so and I heard the change in tone which wasn't what I expected. I jumped up to go over and look to see what may have been happening and before I even reached the machine, the Z Axis hogged itself completely into the material to the point where it stalled the spindle and put it into protect. Ruined the part, ruined the bit, and messed up my custom waste board for this part pretty badly.

So - after getting over the shock of it all and mulling over every detail of that file, I discovered nothing. My measurements were good, my VZ data points were as described and there was nothing displayed in any way to indicate that this might happen. I pulled off all my materials and placed a blank piece of wood on the machine to protect it. Ran the file again with no bit in the spindle and a safety height that would put the spindle nice and far away from the material. Ran the gcode again and guess what - it did it again. I was able to watch the behavior and it was bizarre. I saved the file as a VZU so that I could send it in for analysis. Turned off VZ and ran the file again - it did it again - even with VZ deactivated. I finally reloaded the same file into the software and this time did not do anything within VZ. The file ran flawlessly so I went ahead and completed the pass with no VZ to aid in the cut. I had one more thing to machine on this part and setup for 4 x simple 3mm holes milled to only about 1.5mm deep using pecking. My left to right was a little off so I was using the locating feature of the software to place the bit where I needed it. Brought Z to zero and confirmed location. Started the pass and while it was doing the peck, I decided that I wanted to shift the position a little. As always, I hit the x,y, zero button but this time - of all times - the Z didn't pick up before relocating and dragged the bit straight through the material to get to zero. Part officially destroyed. This all happened with 45 minutes btw.

I mean is the machine possessed or something? lol.
It is frightening when things like this happen as you never know when it is going to happen again. You lose the trust in the equipment.
Anyone else experience these types of unexpected behaviors? To my memory, the only weird thing I have experienced with these machines always seems to happen when I run the PC software. Early days on the thumb drive files, I don't remember having too many head scratchers. Been running the Next Wave machines for about 3 years now so I do have plenty of experience.