Di-Directional Isolator

The most likely cause is a loose connection. They take a big load, and are rated to take that load, but if you have a loose connection that load will look like a big resistor to the conduction of the current demanded. It will overheat, and then heating affects the wires and they will burn and cause corrosion and then not conduct like they should. This will lead to failure. Take the connections apart, clean them up, and put them back together tightly.

And that does mean all ends of the connections, not just at the isolator.