Using https://gltf.report and switching to the script tab (<> symbol on the left), the following script can be used to identify what kind of data the accessors from the error message hold.

gltf-accessor-usage.js

const root = document.getRoot();
// Get all accessors in the document
const accessors = document.getRoot().listAccessors();

// Loop through each accessor
for (let accessorIndex = 0; accessorIndex < accessors.length; accessorIndex++) {
  const accessor = accessors[accessorIndex];

  // Find where the accessor is used
  const usedAs = findAccessorUsage(accessor);

  // Log information about the accessor
  console.log(`Accessor ${accessorIndex}:`);
  console.log(`- Data Type: ${accessor.getType()}`);
  console.log(`- Component Type: ${accessor.getComponentType()}`);
  console.log(`- Count: ${accessor.getCount()}`);

  if (Object.keys(usedAs).length > 0 && usedAs.constructor === Object) {
    console.log('- Used in:');
    for (const [key, purpose] of Object.entries(usedAs)) {
      console.log(`  - ${key}: ${purpose}`);
    }
  } else {
    console.log('- Usage not identified.');
  }

  //console.log(accessor) // Uncomment for debugging
  console.log(''); // Add a newline for better readability
}

// Function to find where an accessor is used
function findAccessorUsage(accessor) {
  const usedAs = {};
  const meshes = root.listMeshes();

  for (const mesh of meshes) {
    // Assume single primitive
    const prim0 = mesh.listPrimitives()[0];
    const indices = prim0.getIndices();
    if (indices.equals(accessor)) {
        usedAs[`Mesh ${mesh.getName()}`] = 'Vertex indices to form triangles';
        break;
    }
    const attributes = prim0.listAttributes();
    const semantics = prim0.listSemantics();  // matches attributes' order
    for (let attributeIdx = 0; attributeIdx < attributes.length; attributeIdx++) {
      if (attributes[attributeIdx].equals(accessor)) {
        usedAs[`Mesh ${mesh.getName()}`] = semantics[attributeIdx];
      }
    }
  }

  const animations = root.listAnimations();
  for (const animation of animations) {
    const sampler = animation.listSamplers().find(s => s.getInput().equals(accessor) || s.getOutput().equals(accessor));
    if (sampler) {
      usedAs[`Animation ${animation.getName()}`] = 'sampler';
    }
  }

  const skins = root.listSkins();
  for (const skin of skins) {
    if (skin.getInverseBindMatrices().equals(accessor)) {
      usedAs['Skin'] = 'InverseBindMatrices for skinning';
    }
  }

  return usedAs;
}