If you see a dialog that display words to the effect of:
Diagram Not Found: Cannot edit diagrams in a draft page, diagram is deleted from the page, or diagram is edited externally. Please, check the page.
- Double check whether the page is currently in draft. If yes, save it and proceed to edit the diagram.
- If you click on the diagram in the space draw.io list of diagrams to open the full screen (lightbox) view, click the "go to containing page" button to locate the page the diagram is attached to:
And try to edit from that page.