This appears to be a result of our apps waiting on SVOX to tell us that it has finished speaking. If you look into your system logs, you will notice that SVOX has encountered a problem and died. Unfortunately, it did not tell anyone else about it!
Fortunately, I think the following is a temporary solution. You need configure the advanced settings for SVOX Classic and disable (uncheck)the box that tells it to "Use Optimized Engine". That seems to do the trick.
Below are some screen shots to help you along.