This is a new issue happened recently, in Canterbury NSW 2193.
My NBN (I am on 100mbps plan) drops a few times per hour during the peak times (after 8 PM). It makes gaming impossible, that the game simply quits with errors. The voice chat also affected to a good degree.
I did ping test against my router also against Cloudflare's latest DNS (188.8.131.52).
The issue appears not to do with my router (apple airport extreme), but Optus's network, as the issue only appears when pinging the internet address.
This is not a wifi issue, as there is a desktop computer connected by wire has the exact the same problem.
I can't see any reported issues in the area I'm afraid. I would recommend speaking with Tech Support on 131344 or via Live Chat so they can investigate your specific connection.