iOs safari 15.4 shows a duplicate model on model-viewer for some GLTF files. Github issue with images: https://github.com/google/model-viewer/issues/3327 Seems to occur only for some files and not all. Unable to ascertain the criteria this happens for.
I suspect this has already been fixed in top-of-tree WebKit with other bug fixes related to multisample resolution, MTLStoreActions, etc. The same problem reproduces on M1 hardware in stable Safari Version 15.4 (17613.1.17.1.13), but is no longer reproducible on Safari Technology Preview Release 143 (Safari 15.4, WebKit 17614.1.7.7).
<rdar://problem/91937165>
We believe this is fixed now.