CallActivity not expandable

Hi All,
the “CallActivity” does not give me the expand option (PLUS sign at the bottom). I have it for collapsed sub-processes, although it is not working either; I can just see it, not click on it. For CallActivity I cannot even see it.
According to the Flowable Documentation it should show it in certain editors/modelling tools. I was at least expecting it to be visiblke and usable in the Flowable Modeler which I am actually using. Any clue what went wrong or is my expectation wrong? Any other editor I shall use?