Maybe you would want to check out the structure I have proposed before using a table of the workflows to be called, then a loop to call them all and JSON information to ‘communicate’ between the main and subworkflows (even if there is nothing to communicate)
the sub workflow needs a start and finish with (in this case) JSON informations coming in and leaving the sub-workflow (I think it could be empty but it could be use it to track the time it took the sub-wf to finish so I can see if it worked at all).
Then it is very important that the sub-workflow are saved in a reset state otherwise they will just be run without changing anything. Mandatory reset I think is only possible in batch mode and with the KNIME server.
Instead of the Input and Output JSON Containers also Table input and output should be possible. Although I have not much experience with that. Instead of using them you could just save the data you want to transfer in a temporary table and reload it in the next step.