Screenshot from my dashboard today. The one with the ~70% error rate is also the one that fails. It has consistently been that unit, and the error rate has remained consistently around that.
Is this a defective unit or something I can fix?
If you haven't done yet, try unplugging the good unit and only let the one with the 70% error rate stay connected to the node. If the faulty board is hashing good now, it's likely a power supply issue.
You could also try swapping USB cables and/or switch the ports on the node vice versa between the units. Principle of exclusion always helps to pinpoint the problem.
If nothing helps, it may be a hardware or manufacturing issue. In that case, best contact the futurebit customer support.