Make sure all of your speakers are up to date by going to Settings > System > System Updates > Check for Updates. Also try unplugging your speakers from power for a couple of minutes and rebooting your router and phone. You can also try re-installing the Sonos app.

Thanks for the reply.

Carry out the above, but the app just won’t allow me to have downstairs and upstairs at the same time. Yet I can pick the speakers individually without any issue, it’s the group function that’s the problem.

Have you called Sonos Support directly to discuss it?

The answer to my problem is simple, out walking my dog Indy and the problem solved. For some reason   I cannot combine two groups, so just make a new group with that works around the problem and it works.