[BUG] Changing the order of elements in the Modeler

[WolfgangDaniel]

We are no sure if the following bug was fixed:

Currently, a fatal error occurs when changing the order of elements in the Modeler. But the error message is only the tip of the iceberg. It often appears as "cannot read property "successorID" of undefined". Unfortunately I can't reproduce the error yet and I can't define an error location (can be the BPMN => SSOT or also the RPAf => SSOT parser).

Please check if you can reproduce this bug. If not possible than we assume that the bug is fixed. If possible, please fix it and if not possible in time then create a proper bug report for this bug including how to create it.

To Reproduce

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2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior

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• Browser: [e.g. chrome, safari]
• JS IDE: [e.g. VS Code, Atom]
• (Version: [e.g. 22])

Additional context

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