Whenever inserting details or schedules from other projects you inevitable get a number of viewports along with them. These often cannot be removed, even though they are not in use anywhere on our sheets. I tried a method using Revit Lookup to find the ids of these viewports but it ended deleting a number of drafting views instead. So needless to say, not a great solution.
Please fix this, as on large projects the number of these can quickly become unmanageable and can often confuse other users as to which viewports to use. I often end up renaming them so they sort to the bottom but this is really a workaround.