AMML reaction objects broken in workflow execution

Execution of the full use case model in workflow mode with the run_model.py script results in the following error message:

  File "/hkfs/home/project/hk-project-consulting/an9294/vre-language/src/virtmat/language/interpreter/deferred_executor.py", line 895, in chem_reaction_func
    return get_chem_reaction, tuple(chain.from_iterable(pars_all))
TypeError: 'Variable' object is not iterable

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/hk-project-consulting/an9294/vre-language/scripts/run_model.py", line 118, in <module>
    main()
  File "/home/hk-project-consulting/an9294/vre-language/scripts/run_model.py", line 112, in main
    prog = run_workflow(clargs)
  File "/hkfs/home/project/hk-project-consulting/an9294/vre-language/src/virtmat/language/utilities/errors.py", line 105, in wrapper
    raise RuntimeError('non-handled exception') from err
RuntimeError: non-handled exception

If the content from sections 09.2 (ORR chemical sub-reactions) and 09.3 (Electrochemistry: Compute U_max and Overpotential) of the use case model are commented out, the workflow executor works seemingly without any problems.

I then tested a simple script which only contains the necessary data to complete the reaction and electrochemistry parts (no electronic structure computations involved). In instant execution mode, the run is completed without problems. However, workflow execution crashes with the same error as reported above. This script is provided as attachmentamml-oxycat_electrochem.vm

Seems like the interpreter in workflow mode has now problems to deal with reaction objects... What can be causing this?