I've been on cable broadband (not NBN) for many years. Normally it is very reliable, but in the last two weeks we've had intermittent outages. They mostly last a few minutes although some have been several hours.
I understand the Optus cable system is now owned by NBN and maintenance may be an issue.
Have others had similar experiences?
It's possible maintenance is the issue. Optus do record all dropouts so they might be able to tell you why they happened. Possibly the modem is giving up. You could request a replacement?
I have an IQ of over 180*. But that one aludes me.
* IQ has been standardised to account for several factors beyond my control, including not being very smart.