On Tuesday morning the Sparky came around to wire up the garage door opener. He choose to hook up the wiring to the same circuit breaker that the ONT, router, switch, AP and SAM Knows box are connected to.
While he did his work he disconnected the power for a short time.
Once the power was back on the internet wouldn't connected. The lights on the ONT, router, switch, AP and SAM Knows box were working perfectly, but there was no internet connection via the AP nor ethernet cable to the PC.
So I logged in to the router, an Ubiquiti ER-Lite, the WAN interface eth0.10 had a public IP address. From the router I could ping 220.127.116.11 but not www.google.com, but pinging 18.104.22.168 and www.google.com from the PC would fail (time out?). I suspected a DNS issue.
Called the ISP, which ran some tests and said the ONT was fine and so was their connection to the ONT. Which narrowed down the fault to the router.
I have a couple of scripts for unblocking geo-restrictions and forcing google safesearch, so I thought the configuration file might have got corrupted, but reloading the configuration file made no difference.
In the end I resolved the issue by upgrading the firmware from v1.10 to v2.04. I didn't try reinstalling v1.10. So I suspect that an extra surge of power somehow corrupted the firmware.
Note, that this entire process to get the internet working again took about 36 hours. 36 hours without Netflix and Youtube during the school holidays, was actually a blessing because the 4 kids went outside for the day!
Is it likely that there was also physical damage router?
(This may or may not be related, but strangely, when I ssh in to the router it says something about the firmware (v2.04), I followed the instruction, but the next time I sshed in I had the same message. I confirmed the router is running from v2.04 and it's the default firmware. v1.10 is still on the router, but just as a backup if required. The router runs fine regardless. Perhaps it's worthwhile getting a spare nano USB with the firmware and config file on it.)