I think you get the prize for the most difficulty with limit switches.
I installed 6 pcs of 1 nF filter capacitors right next to the KFLOP, replaced all the limit switches with ones from Omron- as per the attached datasheet, on which I connected a 2K resistor between Output and Vcc.
I don't see the data sheet.
Also bought the USB isolator you suggested but as soon as I connect it to the KFLOP, KmotionCNC crashes and displays" KMotion.dll Timeout waiting on Action to complete" and you have to kill the process. Happens every time.
Strange the isolator should be totally transparent to the software. Maybe loosing the Earth ground is causing noise problems elsewhere? That message should occur if some Action is not completing. Which Action is not completing?
Removing the isolator, all axis start to work with the inverter on
That would indicate the capacitors eliminated the noise problem.
except when you try and jog toward X home limit switch, which is connected to IO 0 on JP7 of the KFLOP.
Checked all connections and the capacitors for all 6 limit switches and they are identical. No shorts anywhere. When I disconnect the limit switch on IO 0 from the KFLOP, the capacitor stays in place, you can jog toward that limit. Used another sensor, which was working fine on Y, put it on X home but again the axis gets disabled when you jog toward this IO 0 switch. The problem is not the switch, nor the wiring to the KFLOP is checked it many times.
Since you can jog without the wiring but not with the wiring that pretty much proves there must be some problem in the wiring/circuit/sensor.
Note that it is not valid to remove the wiring from an input and leave it floating even with a capacitor connected. It can still float high or low randomly but just more slowly because of the capacitor. It seems you were lucky it floated to the polarity that allows you to jog,
You should troubleshoot why you can't jog when connected. What state does the Digital IO Screen show IO 0 being in? What state does it need to be in to be able to Jog? What is printed on the Console when you Jog? Does the axis disable? What Voltage is the input pin at relative to KFLOP GND?