I appreciate your patience here while I further discussed your case with the team. I spoke to both the dev and QA team but the diagnostics from your Core do not indicate as to why this issue is occurring.
I then requested QA to try to reproduce this behavior on their Squeezebox zone and they have been running it for the last 4 days without issue, both for playback and for volume control.
To us, this indicates that the issue may be something environmental such as your networking setup or possibly another device on the network causing this issue.
I want to try and separate if something on the network is causing this issue, I am thinking that our next step here would be to disconnect everything except the Core + Squeezebox Touch from the network next time this issue occurs. Can you give that a try and let me know if that changes anything?