Just like the IT crowd (https://www.youtube.com/watch?v=t2F1rFmyQmY) sometimes the solution *is* turning it off and on again and that applies to the modem router as well.

We sometimes use various phrases to say shutdown and restart, phrases like; Reset, restart, power cycle or reboot. What is meant by all of these is restart or, shutdown wait a few seconds and then start-up again.

What we DON'T mean is reset the device to factory defaults either via a hardware button or via the web interface.
By the way even if Telstra tells you to do a factory reset don't do it then either unless the helpful level 1 Telstra tech support person is planning to drive to your home or office to re-set it up for you.