mesh deformed when exporting fbx/gltb with animations

I have a rabbit that goes wrong when exporting fbx or gltb. It looks fine in blender but very wrong during exporting with animations. anyone knows why and how to fix it? I have tried bake action, bake ik, new rig with constraints pose, apply modifier before exporting, apply transform, re-parent mesh... scale is 1. rig uses rigify. here are some photos, I can send videos and the file too.

My first blender modeling, rigging and animation... dying to know where i did wrong :(

Thank you..