When connectivity to primary DC fails, WSS Agent automatically connects to backup DC. However, when primary DC becomes available once again, WSS Agent does not reconnect to primary DC - it continues using backup DC.
This is expected behavior. If connectivity to primary DC fails for some reason (e.g. maintenance window) WSS agent will reconnect to backup DC. When primary DC is OK again, agent will not automatically reconnect to it - it will stay connected to backup DC until you manually reconnect or connection to backup DC fails.
Reconnect your WSS Agent manually.