9200 Timed shutdown not working

I have my 9200 set to shutdown overnight at 0400 and restart at 0600. The startup channel is 704 - Radio4. It's been like this for over a year. Recently (I cannot say exactly when) it has stopped working. The box no longer shuts down overnight. I have done a reset to factory settings and set everything up again but this has made no difference. Any ideas why this has started happening and how to make it work properly again? The 9200 is at software level 21 and was updated almost two years ago.