Hi.
I tested 3 app on the same device this morning
App #1) target 22, no runtime permission, MyLocation false in the designer. Black screen
App #2) target 26, runtime permission, MyLocation false in the designer. Black screen
App #3) this is the simple GoogleMap example from the forum, target 21, no runtime but MyLocation enabled in the designer, black screen
uninstalling the GooglePlayServices (removing the update, then terminating it) then reisntalling it, the map come back in all 3 apps.
But my customer says that he already tested this solution last saturday and after 24 hours the map has become black again.