Had this a couple of times recently with my newly purchased Mu-so II. The app reports the above and won’t load. Music continues to stream but I can’t control it.
Only solution is to pull then reinsert the power cord, not an easy process given it’s location. Rebooting via the remote has no effect.
Not invariably in my experience with several, but of course the router is another possibility rather than the switch, and indeed it could also be worth seeing whether a change of Ethernet cable resolves the issue.