After upgrading to 3.10 I discovered that I can no longer send messages to my students. From the participants' screen I select all. However, the drop down menu from which to select send message (and other functions) no longer appears.
This sounds more like a theme issue - have you tried changing the theme to boost and seeing if it appears then?
I never have used themes, either now or before the upgrade. It's now and was before set to the default.