Sonos One won't finish setting up

I have two Sonos One speakers that I was able to set up several years ago when I bought them. I don’t use them a lot, and eventually they lost connection to my system and wouldn’t work correctly, so I am trying to set them up again.

I tried a factory reset and the Sonos App (the latest) was able to recognize it and add it to my Wifi network. Then it says that it might not show up in the System list and I may need to restart the speaker, which I did. After plugging it back in, it’ll appear to boot up normally and get to the white status indicator, but the Sonos App still won’t recognize it. If I push any of the buttons on the speaker, the light flashes red a few times and then goes back to white.

I’ve tried this process several times and always get the same results. I’ve also tried plugging in Ethernet and that doesn’t help. The same problem happens with both speakers.

These One speakers have always been a bit flaky. Is there a sure-fire way to get them configured?