There are some new Google changes that we anticipated nearly a year ago and is not specific to Store Locator Plus.
Effectively Immediately, all new websites that come online as of June 22, 2016 will require a Google Map API key. This is no longer optional. Store Locator Plus has had the ability to set a Google API key since version 4. Go to the General / Server tab and enter your Google API Server Key.
You can learn more and sign up for a key from the Google Maps documentation site.
Any users running Chrome including those using Android based web browsers will no longer be able to auto-detect their location using the location sensor unless the source site is running https. That means that your website must have a valid SSL certificate. If your site URL does not load when you use https:// as the starting part of your web address the location sensor provided by the Power Add On will not work.