Hi @David Blyth.

Thanks for reaching out and welcome to the community! Let me help you figure this out.

To verify, how are these speakers working together, are the Play:1’s used to be bonded with the Playbar as surround speakers? 

If yes, please check the following;

• The products you want to use as surrounds must already be added to your Sonos system as separate rooms.
• If the products you want to use as surrounds are set up as a stereo pair, make sure you separate the stereo pair before adding them as surrounds.

Hopefully, that helps but if not, please submit a diagnostic report and reply with the confirmation number, I'd start by reviewing your system and see if there’s anything causing this issue.

Let us know how that goes.