It looks like Google recently updated their policies on using an API key to access Google Maps. If you're seeing "development mode" map views or pop-up errors saying your maps can't be loaded properly, then you just need to add a Google Maps API key to your Groups Engine install. The good news is that it’s pretty painless to get fixed up.
First, visit the following link, and log in to create an account if you haven’t already.
Visit the Google Cloud Platform site
Second, create the account, update your billing information (mandatory... more on that in a second), and walk through the process of signing up until you can create a project and get an API key.
Finally, once you have the API key, visit Settings > Groups Engine on the WordPress site where you're using Groups Engine. In the General Settings tab, scroll down to the “Google Maps API Key" field, paste your key there, and save your changes. After that, your maps should function like normal.
In regards to billing, Google now includes a bunch of language about free trails, billing limits, etc. 99% of our customers will never have to pay a cent to Google for using the Maps API with Groups Engine. Only folks who have hundreds of thousands of folks a month searching for groups with Groups Engine would ever run into a scenario where they’re having to pay to use Google's API. You can read more about Google's pricing policies here.
One final gotcha... If you’re using any caching software on your site, make sure you clear the cache after all of this, and make sure you clear your browser’s cache as well so that the API key makes it to the live site.
If you run into any trouble, send us a message. Thanks for using Groups Engine!