Since 5.7 we are experiencing Hibernate Session exceptions when accessing CEOs in a Job context (<job /> module in plugin.xml)
The documentation says:
At a minimum, the module class must implement Quartz's Job interface, but for access to Confluence's objects and database you should extend com.atlassian.quartz.jobs.AbstractJob.
But simply extending AbstractJob is not enough. There is no transaction management automatically applied in this case.