Given the quality of your build I doubt you have a bad ground or configuration problem.Thank you for that, nowhere else I looked said use shielded, but I can. Thanks for the link. Even the Hyper 9 canbus wires coming off the connector are not shielded - but the ones come off the Orion are.
I've read the Orion documentation and I've built the canbus as close to that as possible. And, it has worked in this configuration, and the Orion is totally fine. It's only the Slave Hyper 9 that seems to be having trouble - and I'm not sure what to make of that. As the slave gives up and throws and error, the Orion software continues to read the bus no problem.
I strongly suspect your CANBUS wires are acting like antennas and picking up interference from the primary wires ( motor leads )
A protocol error isnt a failure to communicate , its signals the system doesnt recognize showing up on the CANBUS.
Since you need twisted pairs ( and/or shielded ) wires for the entire CANBUS you should correct that first and see if the problem goes away.