Have you upgraded some custom node perhaps? I've ran across similar issues when a new version of a node is not backwards compatible. This can cause a situation where your flows.json file has an old configuration that is not anymore editable from the Node-RED editor.
Or if not, have you installed some new node recently that could cause this without any instance?
Copyright OpenJS Foundation and Node-RED contributors. All rights reserved. The OpenJS Foundation has registered trademarks and uses trademarks. For a list of trademarks of the OpenJS Foundation, please see our Trademark Policy and Trademark List. Trademarks and logos not indicated on the list of OpenJS Foundation trademarks are trademarks™ or registered® trademarks of their respective holders. Use of them does not imply any affiliation with or endorsement by them.
The OpenJS Foundation | Terms of Use | Privacy Policy | OpenJS Foundation Bylaws | Trademark Policy | Trademark List | Cookie Policy