Autosave is a highly useful macOS feature that prevents losing incremental changes to a document you’re working on between the periods when you press Command-S or choose File > Save. As you work away, the current state of the document is updated temporarily. When you close the file, changes are applied even if you don’t use the Save command or keystroke.
But what if autosave goes south?
Some users, including a Macworld reader, have seen the error in various macOS apps dating back nearly a decade: “The document could not be autosaved. Your most recent changes might be lost.” The dialog box explaining this has an OK button and nothing else.