Creating Software with Modern Diagramming Techniques: TypeError when trying to improve readability (page 20)

When I added Title: \n\n as instructed, trying to improve readability of the Title node, I got this error:

TypeError: Cannot read properties of undefined (reading 'members')

This happens both on mermaid.live and using the rendered included in the Obsidian editor (not sure how to find out which version it is)