If any author uses in his theme or plugin this Marker Clusterer library for their maps:
https://github.com/googlemaps/js-marker-clusterer
please note that the contributors have removed the clustering images from the public CDN, thus any clustering will look now like this:
https://googlemaps.github.io/js-marker-clusterer/examples/advanced_example.html
As you can see, no clustering images, only the numbers.
This is the description of the issue and possible fixes if you need to update your Envato items:
https://github.com/googlemaps/js-marker-clusterer/issues/59