If your nodes go offline even if your VPS servers are running, you can try restarting the server and see if they come back online. If they do not, then you will want to destroy those VPS instances and deploy new ones.
In order for your Set Power Free Account to verify your nodes are online and running, the ping data is required from your node running a full 6-hour cycle. Your VPS provider displaying your server as running doesn't mean that your Green Node software is online on that server. We recommend monitoring your node status from the dashboard at https://app.setpowerfree.com/login.