"thanks heaps for running through the troubleshooting"
They didn't? (and can't)
"Generally speaking, an Ethernet connection almost always provides both a stronger and more reliable broadband service"
True, but how is that relevant to a box that keeps turning on and off?
"Give those a shot"
You only mentioned one action?
"I would recommend having a chat to our Tech Teams available 24/7"
Optus should consider that "available" to customers means "contactable". Not the ability to send a one way message that might take a day to get a response from. Perhaps Optus should update their signatures to "available within 24 hours"?
It seems for some of the units they did just come good after time so you could also just wait a day or two. Turning it on every now and again to check.
Other than that unfortunately your only other options at this point are to try a soft and then hard reset. These can usually be done at power on:
If those don't work then Optus will replace the box on request (you just have to be able to get in contact.)