Cannot cancel a transaction with boundary cancel event

I am using a straightforward workflow containing a transaction with a boundary cancel event, like in the image bellow.

The cancel is not working: the engine makes the following exception: org.flowable.common.engine.api.FlowableException: No execution found for sub process of boundary cancel event boundarycancel1

I think it is a bug. It should work according to this piece of documentation : BPMN 2.0 Constructs · Flowable Open Source Documentation .
We have just migrated from activiti. We have a lot of legacy workflows like this which were working just fine with activiti but they are not working with flowable anymore.

Anyone has any idea about how to fix this? I am very surprised as it seems that the flowable engine does not support one of the basic BPMN concepts. I hope I’m missing something.