Tasks Plugin - Group by Filename error

I have an instance of Obsidian on Windows with a Task Code Block which includes “group by filename”

The display of the file name adds a “backslash” so that the “file_name” becomes “file’backslash’_name” which Obsidian warns this file does not exist & click to create. “file_name” does exist.
How can I stop this behaviour?

Thanks

Ian