Rx3i Dual Bus PLC swapping issue

I have a Rx3i Redundant Controller with Dual Bus configuration connected to a Remote NIU(IC200GBI001). I am having an issue that if I swap the PLC from Primary to Secondary controller or vice versa the Remote I/O go to their initial state and then update. What is the Problem. My NIU card is also showing 'Fault' light ON.

Maybe the problem is the "Fault". Fix whatever is causing that and see if your problem goes away.

@RussB
I can't seem to find why the Fault light is ON. Can you tell what are the factors on which Fault is enabled.