I checked your NBN-FTTB service and tests are passing in our portals and has been up and stable for 48hrs.
I have sent a request for a firmware to be pushed out to you.
It is unlikely firmware has anything to do with stability.
I was able to replicate the Internet drop out when running an initial sync of the Ethereum 2.0 Prysm blockchain. about 2 minutes of the sync starting the "Internet" light on the NBN router went out and I lost all Internet access unti lpower cycling the NBN router. After the Internet light was back io nthe NBN router I started the sync again and within a few minutes the "Internet" light was out on the NBN router, had to do another power cycle to get the Internet working again.
Do you need additional info to perform the firmware upgrade? WAN MAC address etc?