If you use your own GeoJSON file for your “Map - Extention” map in Exploratory and the file size of the GeoJSON is large, the map tends to be slow and it may hang in the worst case. Typically, the map rendering gets slower if the file size exceeds 20-30M (depending on how the GeoJSON is constructed though).
You can check out the following note for how to reduce the file size of your GeoJSON files using a tool called “mapshaper”.