No point opening a support ticket because I would just get another unit with the same issue.
I'm about 90% sure that I know exactly why I get this behavior on a firmware update, and some other people don't:
The problem occurs when both devices are power cycled at the same time, and the ATA boots before the Arris router. This is what many people reported last summer, when there were lots of power outages.
So why does mine also see it when the router's firmware is updated? Because I have been using the router's auxiliary USB port to power the ATA, causing it to lose power at the same time, and triggering the bug.
In fact, I am more like 99% sure, because I just tested this as follows:
- Reboot only the ATA. Dial tone is restored in about 1 minute.
- Reboot only the router (with ATA plugged in separately to wall power). Internet is restored in a little over 2 minutes, and dial tone follows immediately.
- Reboot both devices together (with ATA getting power from router). Internet is restored in a little over 2 minutes, as before, but phone still does not have dial tone after several minutes (and based on past experience, will not after several hours), until I reboot it again.
So the lesson is that I can avoid having this problem triggered by the router firmware update if I switch back to using the wall wart for ATA power (which is not ideal given the limited number of outlets on my UPS).
But it will still crop up for many people when they have power outages, which seems likely to happen again this summer, and it would still be better if Sonic and the device manufacturer could address the underlying bug.