Hi Tom 

Thanks for reaching out to the community with your observations. Unfortunately we do not have any official documentation on what kinds of shape CSV files can be successfully imported. An important thing to keep in mind is that this is an experimental feature. It's intended to automate some of the diagram creation process by getting all of your shapes and relationships on the canvas but because of its experimental nature you may have to learn what kind of shape imports work by trial and error and it's likely that you will have to do some manual adjustment and formatting of your diagram after the import. I'm sorry for the inconvenience!

It would be awesome to get this working. I have a situation where I need both horizontal and vertical but after testing a few different things I could not get this working. 

Hi Damien thanks for commenting on this thread! Unfortunately shape rotation is one thing that is not currently supported in our process diagram import feature but if this is something you would find helpful please feel free to submit this feature request form with your thoughts. Our Product team uses the feedback from these forms to understand which changes users would most like to see in Lucidchart so this is the best way to advocate for a new feature.