To export your Google Maps starred locations:
Go to Google Bookmarks: https://www.google.com/bookmarks/
On the bottom left, click "Export bookmarks": https://www.google.com/bookmarks/bookmarks.html?hl=en
After downloading the html file, run this script on it to generate a KML.
It's hacky and doesn't work on all of them, but it kinda works.
@rlewandowski1988, please check your JSON file (open it in a text editor). It should start as:
{ "type" : "FeatureCollection", "features" : [ { "geometry" : { "coordinates" :........
It seems it is missing the "features" section. If your data is not private and if you can share your JSON file, I am willing to help you.