Hi Jason,
I had similar issues, does it only happen on the publisher ? When i experienced the problem restarting the tomcat service cured it. Something to do with it taking all the memory. Try looking through the readme's for the latest version of ccm 5.1.x you will probably find loads of issues which were fixed in the latest version. I upgrade my cluster to the latest ES at the time and this cured the problem.
Hope this helps
Dave