Welcome to our forum & thanks for the question!
Unfortunately, it's difficult to tell what's wrong with a GeoJSON file as it has many lines and thousands of properties that should be analyzed.
We have already prepared a set of GeoJSON and TopoJSON maps that can be used with Highcharts Maps with no problems: https://code.highcharts.com/mapdata/
If you're trying to find out what's wrong with your GeoJSON you could try to compare it with one of the maps that we've included in the resource above.
It's highly unlikely that Highcharts Maps does not work with a proper GeoJSON file, but if it does - please report it here or on our GitHub repository with a minimal demo in JSFiddle.