I think I reproduce the problem here:
And it is fixed here:
Can you try to add this code in your PG and let us know if that fixes the problem:
BABYLON.SceneLoader.OnPluginActivatedObservable.add((plugin) => {
if (plugin.name === "gltf") {
plugin.useSRGBBuffers = false;
}
});
If the problem is fixed, then it could be related to the bug in Angle where sRGB texture loading is using a slow path: see Glb with huge texture load much slower in 5.0.0 - #3 by carolhmj and Added option to force sRGB Buffer support state by RaananW · Pull Request #11758 · BabylonJS/Babylon.js · GitHub.