Um current connections


we have Universal messaging installed in 4 servers say for Server1, Sever2,Server3,Server4.
And all the four in cluster.

When I open UM Entriprise Manager , I could see Current connections of Realms of - Server1 and Server 2 are having a value of 20 but where as the current connections of Realms of -Server3 and Server4 are ‘0’(ZERO).

Could someone please help me in explaining why CurrentConnections Are Zero in Realms of -Server3 and Server4 and how can we resolve it and make Current connections to 20