Bitcoin testnet not connecting to hardcoded ip addresses
These are seed nodes, not nodes that are connected to for a connection. A seed node means that it is a node that will be connected to in order to get addresses of other nodes to connect to. That connection will not be maintained; rather it is temporary.

If you want to connect nodes to each other, you should not be modifying the seed nodes at all. Rather you should be using the -connect=&lt;ip&gt; option (or add it to your bitcoin.conf file) to connect only specific nodes.