Router: Asus RT-ACRH13
2.4G set to 20MHz, channel 11
5G set to all, channel 165
no airtime fairness, WPA2 personal AES, same password for both networks, different SSIDs
I have rebooted my router multiple times during this

When I leave Ethernet disconnected and do a factory reset → S2 set up new system → it finds the Play:3, connects to its WiFi, does its connection chiming → gets to the point of connecting the Play:3 to the house WiFi, then says cannot connect. Selecting the other SSID yields the same result. I am certain the password is correct.

When I connect it to Ethernet and do a factory reset → S2 set up new system → it finds the Play:3, does its connection chiming → still goes to the step of connecting the Play:3 to the house WiFi, but it seems the WiFi chipset is disabled while in Ethernet mode because there are no SSIDs displayed to pick from. “Other network” is the only available option. Selecting that and typing in the SSID yields the same error.

The exact text is:
We couldn’t connect to <network name>. Make sure you’re using the right password for this network. You may need to reboot your router.

I’m gonna add on a little commentary that S2 is absolutely terrible. Sonos ruined their rep with that totally unnecessary switch from simple to unreasonably complex and laden with errors. I *never* had issues with these devices and S1.