I just got a freeze when trying to switch windows. Attached is a sample in case it helps you debug 
Sample of Dorico.txt.zip (30.6 KB)
Amy, it looks like Dorico was waiting for the audio engine, and presumably it had died. If this comes up again, please check whether the VST Audio Engine process is still running in Activity Monitor, and if it is, sample that process as well as the Dorico process.