Looks like your "Divinity Engine 2 Data" may be out of date, hence the story editor errors.
On Steam, this is the DLC under DOS2. Not sure where it's located for GOG, but see if that needs an update as well.
There is no DLC on GOG. We have to redownload the editor!
The version I could download from GOG was released on the 10/26/17!
The latest version was release on 12/5/17!
