Sometimes host is not discoverable

Sometimes I try to register the host machine using custom settings but somehow I am not able to see that host in rancher server. Even when I checked with host machine it says that rancher agent is working on that host machine perfectly. Though other machines can be registered as a host to the same racnher server. Any idea of what would be the issue?

If you reload the UI browser window does the missing host show up? If the UI gets disconnected from the WebSocket that tells it about changes there is currently an issue where it will not always reconnect correctly, so you would not see any server-side changes until reloading.