This last 2 questions are secondary to what happened today. While I was doing a job in 2 cuts, a roughing and a fininshing cut, on both of them, in one or two points, the z axis decided to go upwards and cut in thin air.
This was about 5mm or more in the air. Like it was cutting for 2-3 hours without a problem and then sudently, raise the z axis 3-5 mm above and continue cutting.
I could say to the client: it is cubism, but he.ll not buy it as it looks very weird.
I managed to fix it by rewinding the g code, , restart from an approximate gcode line, rezero the z axis and continue cutting, but that.s no fix.

Any ideas, or links that detail this or a similar problem?