The error you got mostly because the Google Maps API is not loaded yet. Could you please make sure that the init code is executed inside the load action?
Or did you have a plugin that moves the scripts? Could you please try to reproduce the issue on one of the WordPress’ stock themes (like Twenty Sixteen) with other plugins deactivated? If it disappears, then you can activate the theme and plugins one by one to see which one causes the issue.
Welcome to the Advanced Custom Fields community forum.
Browse through ideas, snippets of code, questions and answers between fellow ACF users