There is a deadlock in concurrent cron job execution with release resource option.
Two notebook run with cron job that release resource after job finished.
In Notebook.CronJob.execute() method:
T1. note.runAll(); // locked paragraphs(lock) and wait to interpreterSettings(lock)
T2. notebook.getInterpreterFactory().restart() //locked(interpreterSettings) and wait for paragraphs(lock) during jobAbort.
This will trigger a deadlock that cause zeppelin hang.
Detail stack trace please refer `deadlock_cronjob.jstack`