Hi,
I noted that the connection pool configured in activiti-explorer (file activiti-standalone-context.xml) is dbcp from apache.
This connection pool is known for being affected by some limitation, at least in my personal experience I found that performances rapidly degrade with the number of threads.
I wonder if you've ever evaluated to change the dbcp in favour to something more modern such as either bonecp or hikaricp.
Kind regards,
Andrea