It was 3 years ago so I don't quite remember the details. I think the problem happened due to an update that broke all workflows of a certain type or something, and they had to be recreated (maybe it was related to Split-nodes?).
Anyway, to delete the broken ones we couldn't use the UI (as it fails when selecting them), so I think they had to be removed manually by tinkering with some files on the server. Unfortunately I don't remember the details as we had help from Xerox to figure out how to do it.
I opened one of our Workflows and turned on the new "Maintain Sub Job Order" checkbox. No other changes.
When I saved I got "Internal Server Error".
Now, whenever I try to select that workflow (under workflow setup) I just get "Internal Server Error". This makes it impossible to Copy/Edit/Delete the workflow (as when i close the error it selects the next workflow in the list).
I can still submit jobs to the workflow, but they don't process properly ("0 pages") and doesn't get sent to the printer (although they end up in "completed").
I do not know if the "Maintain Sub Job Order" checkbox was related, as I tested to turn it on on another workflow that should have been effectively identical (it was based on a copy), and that worked fine.
I will talk to our Xerox contact, but figured it was worth posting here as well in case anyone else has experienced this.