hook wpgmp_markers overridden by filter

I’m using wpgmp_markers hook to customize the marker icons used on the map as follows:

add_filter('wpgmp_markers','wpgmp_markers',100,3 );

function wpgmp_markers($places, $map) {
	foreach ($places as &$place) {
		$place['location']['icon'] = 'my-custom-icon.svg';
	}
	return $places;
}

This works as expected during first load however when a filter is applied, the icons revert to their category icon. How can I get my change to stick?