There have been several updates, each improving the situation. Maybe your issue has been resolved. More updates are scheduled.

Well I am happy now - a Sonos tech booked a call in Western Australia, signed into my PC and I now have a new music folder and most of my library moved across and he stayed on line to listen to ensure it worked, Then showed me how to add tracks to the new folder in case some were not in the folder he had made. I have just added what was an older iTunes library and it worked so most if not all of my music is available again. Thank you Marx A from Sonos.

I’m finding it hard to navigate within speakers and to find music. The links do not seem to be intuitive. Also, the Sonos system keeps losing it’s WiFi link. When I do find how to change speakers and/or music, it seems very clunky, with a delay of several seconds between actions. I have often pressed a second time not realising that there is to be a delay. I now have to - press once - wait, before another action.

Also, can I update app manually? If so, how, please?

There’s a Systems Update option on the Manage page of Settings in the App or you can do it from the Play Store.

To play music on a specific speaker/room:

Home screen - touch the name of your system top left (or drag up the Now Playing shape from the bottom). This brings up all of your available speakers. 

Tap a speaker you wish to play music on. This then becomes the active speaker.

Select music to play. It will play on this speaker.

To play on multiple speakers simultaneously:

On the Now Playing screen (or on the Now Playing section at the bottom of the screen), tap the icon that shows two speakers in front of one another. This brings up the grouping screen. 

Tick/check each speaker you wish to group. Tap Apply.

Any music you select will then be played on these grouped speakers. 

(Untick/uncheck the speakers again to remove them from the synchronised group.)