How to reference external JS callback in custom module
You could/should add the defer tag to your maps drupal_add_js as recommended by google (https://developers.google.com/maps/documentation/javascript/tutorial)

You'll get abit better page performance and should get rid of your issue you're facing as the google maps code will always be loaded after your scripts

Here's how you can add the defer tag:
How to drupal_add_js an external and defer script