yes, that is true that there are quite a few queries in there though only 8 of them are affected - all that use elements. Though I linked only the first which is the simplest for reference. If you'd like I can link all of them here... but I think the solution will apply to all of them.

Regarding the "valid JPQL", might be I used that to positively as users of jBPM reported to run it with other JPA providers thus that statement

So the her lis what we have:
Task has an embeddable PeopleAssignments [1] that in turn has different collections of assignments where one of them is potential owners [2].

[1] https://github.com/droolsjbpm/jbpm/blob/master/jbpm-human-task/jbpm-human-task-jpa/src/main/java/org/jbpm/services/task/impl/model/TaskImpl.java#L93
[2] https://github.com/droolsjbpm/jbpm/blob/master/jbpm-human-task/jbpm-human-task-jpa/src/main/java/org/jbpm/services/task/impl/model/PeopleAssignmentsImpl.java#L49

Please let me know if you need any more information, I'd be more than happy to provide all that I can.