Depends on how the two SCADA systems are configured. Are they two stand-alone stations where each has it's own I/O server, or server based, where the clients use the I/O server of the server system.
If you have a server based system and the problem occurs only on the client, maybe this is a problem with the client-server connection.
If it was a problem with the number of plc connections, then you would not see any green variable. The DASSIDirect server uses only one connection to the plc. If this connection fails, all variables would go to status bad (red in system management console).
If you are using the ressource 03 for the S7 connection in the connection setup in the system management console, then you don't need to configure anything in Simatic manager.