Icon Map not working

Hi,

I was trying to build a visual with the customised visual "Icon Map" that can show location's geofence in circles using lat,long and diameter in meters. It worked fine at the first but when I switched to a new page and came back to the visual, map just became something like this in the screenshot.  

I've tried to delete the visual and restarted again. And again it worked fine at the start, published online then the visual just cannot work.

Does anyone know how to resolve this issue? Many thanks!