leaflet geojson coordinate problem

I wouldn't call it a bug, just a matter of confusing and contradictory standards.

When talking about geographic locations, we usually use Lat-long. This has been codified in the ISO 6709 standard.

When dealing with Cartesian coordinate geometry, we generally use X-Y. Many GIS systems, work with a Geographic Location as a special case of a 2 D coordinate point, where the X represents the longitude and Y represents the Latitude. This order of coordinates, is exactly opposite that of the regular Lat-long notion.

Coming to your problem:

The map.setView takes a l.LatLong as an input, where the first cordinate is a Latitude, and the second is Longitude.

Hence when you want 52.23N, 4.97E, you pass in [52.23943, 4.97599]

The GeoJSON standard says that for any point, the first parameter is the X Coordinate (i.e. Longitude) and second parameter is the Y coordinate (i.e. Latitude);

Hence when you want 52.23N, 4.97E in GeoJSON, you need to pass [4.97599, 52.23943]

For further reading, go through this Q&A