Random Z-Axis plunge

[JAZZCNC]

Ok first lets clarify the difference between controller and drive. The controller is the software that commands the drives which run the motors. Each motor will have a drive (The things with dip switch's on).

I'm pritty sure it won't be a Drive problem.! Drives usually just work or they don't. . . Same with motors.!

It's more likely 99% to be either a lose wire or electrical connection, partly broken wire etc.? . . .OR . . .It could be electrical interference "Noise" from some other device thats nearby.?

"Noise" can be do all sorts of crazy things to a machine,false E-stops, twitching motors over running motors etc and it can be a night mare tracking it down.
Often it's because of poor grounding or earthing practices within the controlbox or just crappy electrics in general.
It can come from simple things like the radio or washing machine or the actual CNC machine it's self. The VFD from the spindle is Num1 candicate for noise.

I wounce had an issue with noise tripping my machine at random times, it went on for months. I went for all the usual suspects, dodgy connections,signal wires running too close to power wires even replaced relays that looked Iffy but still it happened.???
Then one day my son noticed that it always seemed to happen the same time the compressor shut off, OFF not when starting.? The compressor was in a box outside but just the other side the wall to the CNC machine.! He was correct it was the contactor which was on it's way out and producing noise, changed it and problem went away.!!
It had to be noise because the compressor was on a totally different circuit because it was such a big compressor so needed lots of juice so it wasn't feed back thru wires but the machine was close enough to pick it up and trip the E-stop.

Now I'm not saying yours is noise becasuse I'm pritty sure you have a lose or partly broken wire, or trapped wire.!
My advise would be start with the wiring and check every wire on the Z axis drive,motor and BOB connections then along it's length for pinchs or crush marks, tight spots in the cable chain are favorite spots, entry exit points etc.

It won't be a drive problem I'm fairly confident of that and I'm sure it won't be a software issue if the codes run ok before. (Unless there's a known Bug in the control software.?)

IF still doing it after all that checks out ok then I'd look to the control box it's self and the wiring grounding conditions.! . .Things like:
Does it have shielded cable for all signal wires IE: to motors, limit switchs etc.?
Does it use Star grounding.?
Does it or the components even comply with EU regs.? Could be sub standard and poorly made easily interered with noise wise or even produce noise.?

Good luck and keep us posted.!