I have a similar problem. I have tried all the remedies suggested, but still can't get Z to go down on jog. All axes work fine on fast jog (with shift key). X and Y work fine in standard jog. Z works upwards on standard jog, but when you try to jog down you get no movement and all axes lock out, requiring a manual reset to get anything going. I have reversed polarity of Z direction pulse (to eliminate possible mechanicals) and the problem reverses, with requested upward movement causing lockout. I suspect this may be linked to THC, but I have disabled THC inputs and it is still the same. Under program control Z axis moves on G0 commands, but on THC (PROMA) it shows a request to go down, but no actual movement.
Any ideas please.