Hi Ian,

  We have responded to this through support since it involves specific details w.r.t to your environment.

These problems generally arise because of connectivity issues and credential problems. One problem could be which ports to allow which is documented here as a KBase.

https://support.site24x7.com/portal/helpcenter/articles/i-have-installed-on-premise-poller-in-my-secure-network-which-ports-do-i-need-to-allow-access-in-such-a-scenario

Other reason could be because of incorrect credentials or device templates being associated with the devices

https://support.site24x7.com/portal/kb/articles/troubleshooting-steps-if-the-network-devices-are-being-discovered-as-unknown

-Jasper