Importing issues?

Some of my models appear to be broken with their rigs and mesh when I import them, but this is not a problem inside the modelling program.

The model in Sketchfab:
Screenshot 2023-02-28 174651
The model in Blender, where it was originally made:

Is there a fix to this?

Also this occurs with some of my humanoid models with rigs as well, where the animation previewed in Sketchfab often bends the limbs in mysterious ways, especially the hands.

hi, did you try reset the scale on the parts that are glitching, i “think” this might be related to parenting/armatures of child mesh with certain scale attributes. I am not sure what causes it other then i have had a similar issue before that resting scale seemed to resolve on certain mesh

Supplementary to the remarks by @Tycho_Magnetic_Anoma you could try to export your model as glTF 2.0 (.glb/.gltf). Sketchfab copes excellently with this format.
However, since this export always triangulates automatically, it is better to carry out the triangulation yourself beforehand. This is in case the automatic triangulation creates unexpected artefacts in the textures or the normal map.

If you’re using FBX, I have found that applying all transforms to your models before parenting to the rig can help. Also I make sure to save the blend file right before exporting and also doing a cleanup to get rid of any extra meshes, materials, etc you might have generated but not used.