Good morning Tom,
But a stepper cable with a cable break can fail randomly, which means it works most of the time and then the motor makes wrong steps. It can even run into the other direction if one single wire inside is affected in one moment.
How can you be sure it’s EMI? I believe this is extremely difficult to distinguish from other causes impacting the electrical signals inside the cable.
me too, but the molded-on connector housing are just a strain relief for the crimped pins. They do not prevent that the unreliable Molex connectors are subject to movement (at the left end of X axis) which is nothing that they are made for. I would in any case, if you have the opportunity, 3D print a strain relief that fixes the cables way before the connector.
The best way to eliminate such problems would be to retrofit a serious cable management, which would mean print or buy a drag chain. I remember that @TMToronto made his drag chain 3D print files available here because at that time I had the thought to use them, later he bought a drag chain from IGUS.