From what you have mentioned, it sounds like you have an NBN Fibre to the Premise (FTTP) connection type. The NTD (NBN box attached to the wall) itself has 4 available UNI-D ports, have you tried connecting to the other UNI-D ports as well to check if this would resolve the issue?
I have also attached the link to the Quick Start Guide: NBN Fibre to the Premises (FTTP) for you in case you require it.
If you are still needing a hand, please contact our Technical Support teams via the My Optus app for further assistance.
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