If you are using an Android device, read this thread:

I think this is possibly a ‘known issue’ (reported elsewhere on this forum) and that Sonos/Apple are currently investigating this matter, which is related to some Android devices.

I understand it’s a case of perhaps trying to use a different mobile controller device (iOS devices are working okay) for now, or maybe waiting for the fix, but there’s no telling how long that might be before it’s sorted. 
 

Here is a link to another thread with a response from Staff …