It never came back and Christine spent hours trying to sort something out. She didn't set it up so i don't know how much she understands of how i have it configured. She managed to get very frustrated and she came to bed at 3:30 am. I woke and couldn't fall back to sleep. I did have a strategy to try with the network, so i got up around 4:30 to give it a go. Also, i needed to get the bedding in the dryer.
While working on documenting things and preparing a fall-back configuration, i determined that the router works when my laptop is plugged into ethernet (which we set up some time last week) and then stops when i unplug my laptop. This explains a certain amount of the intermittent failure as my work laptop is generally plugged in, but not always. The longest outage was when i went to work on the deck last Friday. Usually my work laptop just sits on the desk plugged in, so usually the wifi was working. I occasionally swapped out my personal laptop with the work laptop to do video at my desk, so that would have created some "outages". And when there was an outage, i was using the ethernet connection to bypass wifi to simplify trouble shooting and everything started working again. No wonder i felt gas-lit.
So, i've turned off the router, and set up one of the two wifi signals on the modem to use the same SSID and password as the router: most systems should just switch over to the modem's network with no effort. The other wifi signal i've given a clear name and that can be used when i turn the router back on to help troubleshoot.
OY. Now to go care for Mom and get Dad a break.
This is also posted at https://elainegrey.dreamwidth.org/804074.html .