We have experienced electrical interferences on some of the first machines produced, which we had never seen on prototypes. This is especially true for the left cartridge holder.
We have an easy fix which consists in splitting the rubban cables linking the three elements of the cartridge holder (RFID, endstop, motor) to the zimboard.
NOTE : You must of course make this modification while the printer is switched off.
We have shown on the picture the before and after shape of the cables.
IMPORTANT NOTE : just splitting the cable is not enough, you must separate the path of the motor cable (which have fairly high intensity current going through) from the two other cables. We suggest you have the motor cables pass below the zimboards and the RFID and endstop cable over it.