I think it's a bug in jBPMN 5. Tried in versions 5.0.0 to 5.1.0.M1.
In a embedded subprocess I add these nodes:
<property id="_3_Property" itemSubjectRef="_personsItem"/>
<dataObject id="_3_DO" itemSubjectRef="_personsItem" name="DO_2"/>
then, in a Task within the subprocess I am using
<dataOutputAssociation id="_12">
<sourceRef>Dout_3-2-2</sourceRef>
<targetRef>_3_Property</targetRef>
</dataOutputAssociation>
or
<dataOutputAssociation id="_12">
<sourceRef>Dout_3-2-2</sourceRef>
<targetRef>_3_DO</targetRef>
</dataOutputAssociation>
I am getting "Could not find variable scope for variable _3_Property when trying to complete Work Item ..."
"Could not find variable scope for variable _3_DO when trying to complete Work Item ..."
In fact when I dump the process via XmlBPMNProcessDumper, neither Property nor DataObject is even there under Subprocess.
the full BPMN file attached.