If you embed Google Map in your website or application, you’ll have to place it outside of hidden tab; Or you’ll need to add a trigger in JavaScript to load the map; however, visitors of your website must double click to fully load the map.
You can add this trigger like this on the page: google.maps.event.trigger(map0, ‘resize’);
Or you can add a function call to Click event of a map tab:

$( "#TabIDHere" ).click(function() {
google.maps.event.trigger(map0, 'resize');
});