Iconlist not visable

please turn on debugging in wp-config.php and also have a look at the php error log which might give you additional infos why the icon list is not displaying. I assume this is related to a folder/file permission issue on your server, not allowing the plugin to read the icons at /wp-content/uploads/leaflet-maps-marker-icons.
It could also be that your hoster has additional security configs in place which also prevents the according code for icon listings to run….