Typically, from my understanding of how its redirection works, is that it is likely an IP issue (something like the device may be on a manual IP) or a modem issue.
I would check the IP address settings for the computer, if they are manually assigned, try change it to dynamic, if it is dynamic, try change it to manual and try a manual IP like 10.0.0.137 since 10.0.0.138 is the gateway itself.
If that doesn't work, it would be to try a hard reset of the modem, and if that also doesn't work to talk to NBN Assurance who may send a replacement modem if they feel that is the cause.
I would check the IP address settings for the computer, if they are manually assigned, try change it to dynamic, if it is dynamic, try change it to manual and try a manual IP like 10.0.0.137 since 10.0.0.138 is the gateway itself.
If that doesn't work, it would be to try a hard reset of the modem, and if that also doesn't work to talk to NBN Assurance who may send a replacement modem if they feel that is the cause.