It’s possible that the fault lies in the Muso firmware, but other possibilities are that someone who has previously used Spotify Connect is inadvertently streaming it to your Muso without realising it, or that interference is sending a signal to the infra red remote input.
The Spotify issue is a strange one which occasionally catches people out. Anyone who has previously used it through your Muso can accidentally do so again without being anywhere near your network.
Worst case scenario: you’re in bed, your kids are out at a party and want to play some loud dance music. They haven’t noticed that your Muso is still selected as the output device in their Spotify app, and when silence ensues they hold their finger on the volume button until it hits maximum.
The fact that this is technically possible is down to a known quirk of the Spotify app which they refuse to change, so it’s out of Naim’s hands.
I’m not sure a factory reset will make any difference. The solution is to get the person who is inadvertently doing this to go to the settings in their Spotify app and get it to ‘forget’ your streamer.
No, once someone has used Spotify Connect to stream to your device their Spotify app remembers it. The only way to prevent someone from accidentally sending the stream to your device is to make sure they don’t do this, or to get them set their Spotify app to forget your streamer.
Otherwise, as long as your device is turned on and has a network connection, they can access it.