Is it always the same one that is acting haywire. When you changed the primary ( first unit plugged into controller) did it change which unit was acting up? If it is always the same unit I would assume the circuit board on that unit is defective, if it changes based on how they are plugged into the controller it would be a controller issue. Do you have the latest firmware on the controller, probably wont help much but I am guessing that will be one of the first thing AI tech support is going to ask. Keep us updated on how AI tech support responds, I haven't read to much about failures so Tech support may not be truly tested.