CS1 not showing up as replication partner

Hello Dear Community Members,

I'm really stuck with one issue and looking for some support.

Our VNX5500 unit was working fine for last few years. Now when we take Putty session to CS0 and getreason output shows only Slot_0 Primary Control station and Slot_1 Secondary Control station not showing. We have confirmed that the IP's configured in the CS1 are able to ping from our test system. CS1 not showing from the Unisphere also.