Maybe try importing the scene back into Blender and see if the scene is visible and working as expected there? That would help eliminate the possibility that the gltf file itself is the issue.
In Godot, you could try selecting the MeshInstance node and pressing the "F" button to focus the editor view on it. It should rotate and zoom the camera so it covers the AABB of the model, which (hopefully) will allow you to see the mesh and what is going on.
