Room disappeared

A strange thing happened last night. Put my two kids to bed and one started music on her Play1 (they like to fall asleep to music). This was done in the normal manner using the app. Music played as expected. The other daughter then asked for some Xmas tunes, so searched and started playing a Xmas album from our music library, again in the normal way using the app. The Xmas music was a bit loud so tried to turn it down using the iPad physical buttons. The volume indicator in the Sonos app moved as expected but no change was actually made to the volume of the music coming from the speaker. I tried a few times with no effect. The app then locked up and was not responding to anything at all. The Xmas music then stopped on its own. I decided to close the app down (double click home button and swipe up as usual on iPad) and try again. When I reopened the app the room had completely disappeared from room list. It was also not listed on My Sonos system in settings. This had no effect on my other daughters room and her music continued playing through all this. I managed to get the room back by powering off the speaker for a couple of minutes and then powering back up. The room then appeared after a couple of minutes and my daughter was able to have her Yuletide tunes! All my speakers have allocated ip addresses as I know this can cause problems. We have had Sonos and been very happy with it for a couple of years but the app has been a little buggy since v8. This is the first time we have lost a room though. Interested if others have had this problem and if they know what caused it for them? Is it a symptom of something wrong with my setup?