Hello Rahul,

If your statement (the running system goes to off condition) means that CPU goes into STOP mode (and SF LED is ON for sure), Please make sure that you downloaded all error OBs to your CPUs.
This is just for preventing CPUs from going in STOP mode.

Now, I suggest that you upload your diagnostic buffer, HW configuration and User program here so people can check your problem.

I just want you to make sure that at normal operation the redundant link is active.

Check the status word.

I want to know if you make this test after fault or you just test it as the first fault.
I mean, Do you always switch IM's of the 1st rack then switch the second? or you tried to switch the second rack IM suddenly and suffered from the same problem?
I hope you are just considering that in Software Redundancy, only initial faults are managed.