MKMapPoint distance method sometimes returns nan

I have a curious issue. I have a set of map points, and I'm trying to find the limits so I can create a snapshot (in swift).

I iterate over the set of points and find the max/min of the latitude and longitude values.

I then use these to determine width and height. This works great on a set of data once, but if you run it again (on the same set of data) I get -nan for width.

i.e. if you find min latitude, min/max longitude, then use these values to create mappings and calculate distance, you sometimes get NaN.

If I take the exact numbers (I debugged and confirmed the data is not changing) and put them in a test, it always fails with NaN

This always fails:

   func testCalc() {
      let minLatitude:CLLocationDegrees = 37.330144359999998
      let minLongitude:CLLocationDegrees = -122.04162370999998
      let maxLatitude:CLLocationDegrees = 37.33773012999999
      let maxLongitude:CLLocationDegrees = -122.02319471999999
      
      let pointsPerMeter = MKMapPointsPerMeterAtLatitude(minLatitude)
      
      let minPoint = MKMapPoint(CLLocationCoordinate2D(latitude: minLatitude, longitude: minLongitude))
      let widthPoint = MKMapPoint(CLLocationCoordinate2D(latitude: minLatitude, longitude: maxLongitude))
      var width = minPoint.distance(to: widthPoint)//meters
      var oWidth = widthPoint.distance(to: minPoint)//meters
      var height = minPoint.distance(to: MKMapPoint(CLLocationCoordinate2D(latitude: maxLatitude, longitude: minLongitude)))//meters

      // width will be NaN here [oWidth will not]
      XCTAssertTrue(width>0)
      width = minPoint.distance(to: MKMapPoint(CLLocationCoordinate2D(latitude: minLatitude, longitude: maxLongitude)))//meters
      XCTAssertTrue(width>0)
   }

I'll further note the minPoint and widthPoint are valid, but the distance calculation is NaN. If I reverse the two points (oWidth), it calculates correctly.

I guess I'll phrase this as should this be reliable, are there limits or ways to determine when it will be wrong?