Any chance that the IP address of your VM changed, and that’s what broke Multiroom? It might explain the facts you describe.
I’ve been haunted by this thought of yours:
I have been poring through /volumio/app/plugins/system_controller/volumiodiscovery/index.js, which is the file that was edited in this fix:
and while I have nowhere near the JS chops to figure it out, that piece seems to rely at least to some extent on IP addresses for multiroom function
When using the Web UI, the displayed multiroom devices will all have different hosts from the web client looking at them. But the touchscreen/internal UI may be a special case.
When your local device is displaying its own interface, it’s just looking at itself, but it may not be looking, as far as a superficial search of index.js reveals, at 127.0.0.1, even though other parts of the project refer to 127.0.0.1 for local content. If localhost changes IPs, I could see multiroom on the device not handling this special case well, and looking for something that’s no longer there, explaining the jump to the twilight zone.
I admit this hypothesis could be 100% wrong.