The probing problems I have had with Mach4 are enough to make anyone crazy. I have a different controller (Galil), but it will make you go mad. The best advice I’ve seen is to try a gcode probing routine to see if that works. If so, it’s a Mach script issue. If not, it could be any number of things including electrical noise issues. If it works fine one day and stops working the next, then you are in the same boat as I.