I just installed the latest iOS app version and it has to be said…
The latest version fixes most, if not all, issues I had with the new version.
The volume control is now very responsive - as good as before - and I do not get all the nasty error messages that were popping after whatever action I did.
I know it should not have happened in the first place but, Sonos does deserves credits here. It is back to the stable app I used to have.
Thanks.