If one is editing a page in VisualEditor, and one clicks on a graph that has a type such as "treemap", and then clicks on the "Edit" button to edit the graph, VisualEditor mostly stops working.
Scrolling is no longer possible, the "Save page" button no longer works, "Insert media", "Insert template", and "Insert code block" don't work, the undo/redo buttons neither work nor even update appearance, "Options", "Page settings", etc. no longer work. Things that do still work include basic typing, bolding/italics/other formatting, and links.
The error message is "Uncaught TypeError: Cannot convert undefined or null to object" (from ve.dm.MWGraphModel.getPipelineFields).