form.json won't open

Check for a JSON syntax error (a trailing comma, an unclosed brace); the Script Editor doesn't check JSON as you type. A project that fails to load shows an error on the Input Form.

Autocomplete isn't suggesting anything

The field needs an Autocomplete Key in the Form Editor, and autocomplete.json needs a matching key with at least one value.

My preset changes disappeared

Presets, like everything else, live in the project's working copy. Use Save in the main menu to keep them.

There's no Print button

Print isn't available in the web app. Use Save, then print the PDF from your PDF viewer.

For a computed value that doesn't show up, or a block that renders nothing, see Debugging.