Once I play everywhere I cannot make Alexa control individual rooms

I’ve spent hours on this now.

I have an alexa-enabled sonos one and from there I can command different rooms (I have a One in the kitchen, a One in a kid’s room, a Play3 in the dining room, Play5+sub in living room and a Play1 in bedroom) to play music, but once I ask for a song to be played everywhere - and it indeed does play everywhere - I cannot get Alexa to go back to controlling just one room (even though it replies to say it is). The only way around it is to open the sonos controllers and ungroup the speakers. In fact, I think once there has been any grouping (lets say I grouped two rooms in the controller) I cannot get control over one of those rooms on a individual basis again.

Any advice would be very gratefully received.

Thanks

Jed

edit: It seems I can break grouping as long I stop the music playing in that group and then go to command one of the speakers i.e. I cannot split the group up when it is playing music.

edit: the above edit seems unreliable fix. Doesnt always work. This is infuriating!