VNDetectTrajectoriesRequest not "seeing" ball in video

I am attempting to write an app which captures the flight of a ball from the iPhone's video preview, but I need some help.

I am using the following code:

request = VNDetectTrajectoriesRequest(frameAnalysisSpacing: frameCnt, trajectoryLength: trajLength, completionHandler: completionHandler)` 

to initiate a request to capture a "ball" from a videoPreview.

In the "completionHandler" I use:

 guard let observations = request.results as? [VNTrajectoryObservation] else {
            //print("observations not set up#######")
            return
        }

to capture observations.

In the video capture setup I am using captureSession!.sessionPreset = .hd1920x1080

In the AVCaptureVideoDataOutputSampleBufferDelegate, I am using

trajectoryQueue.async { [self] in
                do {
                    try sequenceHandler.perform([request], on: sampleBuffer, orientation: .right)
                } catch {
                    print("VNSequenceRequestHandler perform error: \(error)")
                }
            }

I have also tried using VNImageRequestHandler to "capture" observations in the Delegate.

A ball is "seen" only if the "ball" is rolling on the ground. If the ball in "flying" or "bouncing" no "observations" are provided. I have tried different FrameCounts & trajectory lengths with no effect.

I am now developing the app primarily using an iPhone 14Pro running iOS 26.3.1. It should be noted that I started development using an old iPhone 6plus running iOS 15.7 with captureSession!.sessionPreset = .vga640x480. and I did get some good results.

If I try the VGA resolution on the iPhone 14pro, I still see no ball flight.

The basis for my app is software from 5 years ago, so I'm hoping that there has been some development on ball tracking since then.

Thanks in advance for any help/suggestions.