What kind of file is it? And was it created manually or by your code? Some file types don’t get shown in the editor and files within hidden directories aren’t shown either - see https://glitch.com/help/hidden-files/. Note also that programmatic changes to the contents of a file won’t show in the editor unless you run ‘refresh’ at the console. They’re still being made - it’s just the editor doesn’t auto-sync and show those changes.