you may proceed with error diagnosis by disconnecting the stepper, but I’m sure it’s the cable or the connector of the cable.
As I think I already stated earlier, these tin-plated Molex/Amphenol Connectors used on the Onefinity are the first thing I will throw away when I will receive the machine and replace them with decent gold-plated industry standard circular connectors.
These tin-plated Molex connectors have been a disease in computers since decades, can’t say how many data loss they caused, and they’re still there, e.g. as ATX power supply connector. The problems that this causes, of which I can report from many years of experience, are in my opinion not at all appropriate to the requirements for the reliability of computers. It’s just money-saving on the part of the manufacturer.
Tin-plated contacts are tolerable if they are plugged together exactly once. Disconnecting and reconnecting them causes problems. Tin is not very hard and the problem is that the wear and tear that occurs with every mating cycle leads in the long term to the contact coating chafing through, exposing the copper alloy underneath, which is even more susceptible to corrosion. And even without touching, the tin itself oxidates with time (and tin oxide is no more a conductor).
I’ve been following this forum since March, and the problems with the cables and connectors keep coming up from time to time. But at least Onefinity seems to have very good support!