I’m equally confused, as it should ‘just work’, so I’ve got some questions.
Are the two PLAY:1s already set up as another room? Or are they currently not part of your Sonos system?
It’s been a few months since I re-added my PLAY:1s back to my Arc, but it worked when they were set up as another ‘room’ in the Sonos system. Since they had previously been connected to a PLAYBAR, they were already set up. I’m wondering if you need to complete the intermediate step of adding them as a separate room first…
But I’m completely guessing here. I’d certainly suggest a reboot of your router, to refresh the DHCP table, but that’s a low level of possibility. Wouldn’t hurt, but may not be the answer.
I would also recommend that you submit a system diagnostic , and call Sonos Support to discuss it, or post the diagnostic number here for a Community Moderator to pick up.
There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.
When you speak directly to the phone folks, there are more options available beyond just the diagnostic analysis.