Hi,
I’m not sure, but it sounds like a permission issue. Please try this in the console (hit F12 > Console) for the user this does not work for (run it in the console when the list item is open either in DispForm or EditForm, and do not open it in a dialog because it is more difficult to attach the console to the correct form):
spjs.utility.getItemByID({ "listName": _spPageContextInfo.pageListId, "id": spjs.dffs.data.thisItemID, "viewFields": ["CreateTask"] }).CreateTask;
Change CreateTask with the internal name of your workflow column.
What is the output in the console when you run this snippet?
Alexander