this usually happens when a connection is temporarily is lost and the automatic transmission of the changes to the server failed. It can also happen when an authentication expires. If that is valuable information not to be lost, I’d double check on a different device, if the changes have been taken into account by the server.
After that it depends on the system, the apps, the browser, the connection. But just with authentication on a browser, it can help to authenticate and navigate on a different tab to verify this is ok. Then you can try to save the changes again.