The function "Add symbols of child elements" is currently only available for a Main-Sub Process hierarchy. If a Sub-Process is added or deleted under a released Main Process, the graphic can easily be updated via this function.
This is deliberately not available for a pure Sub Process hierarchy (Sub Process below Sub Process). The reason for this is that the superordinate Sub Process is not only a structuring element, but also contains modelled contents and corresponding change options could have undesirable consequences.
As a workaround, it is possible to update the graphic as follows after creating a new sub-process in the navigation tree:
1. insert interface
2. create a process reference to the newly created process