Power button on screen not working

Squeezebox Touch screen power "button" in the top left of the screen no longer turns off the device. That portion of the screen is working fine as when listening to Spotify, say, the back button in the same portion of the screen works fine. Tried putting LMS back to 7.8, no change, so back on 7.9.

The only way I can find to get the Touch to switch off is to pause a stream (radio or Spotify) and let it auto switch off.

I can't see anything about it in this forum.

Any ideas anyone?

Thanks,

David