Displaying a DICOM dataset as 3D representation

Question

I am trying to show a DICOM Series as a 3D representation. It worked with a different set of data but with the current one, the 3D image does not show up. The output values in the datastack of windowCenter and windowWidth are -964 and -664. I am using the latest version of AMI.js but still cannot display the DICOMs as 3D.

Do I have to convert the negativ values somehow, so that they turn out as positive values? Or do you have any other idea why I cannot display the Data?

I am loading the Data with the AMI.VolumeLoader, here is the important bit of code:

let loader = new AMI.VolumeLoader();
  loader.load(files)
    .then(() => {
        let series = loader.data[0].mergeSeries(loader.data)[0];
        loader.free();
        loader = null;
        let stack = series.stack[0];

        //stack Helper
        vrHelper = new AMI.VolumeRenderingHelper(stack);
        scene.add(vrHelper);
        //LUT
        lut = new AMI.LutHelper('lut-canvases');
        lut.luts = AMI.LutHelper.presetLuts();
        lut.lutsO = AMI.LutHelper.presetLutsO();
        //update related uniforms
        vrHelper.uniforms.uTextureLUT.value = lut.texture;
        vrHelper.uniforms.uLut.value = 1;

        // camera
        let centerLPS = stack.worldCenter();
        camera.lookAt(centerLPS.x, centerLPS.y, centerLPS.z);
        camera.updateProjectionMatrix();
        controls.target.set(centerLPS.x, centerLPS.y, centerLPS.z);
    })
    .catch((error) => window.console.log(error));

A different set of Data is showing as it should be:

The other set of data is just not showing up and I don't even get an error message.