I don’t see this problems in most of the models that I use. In the ones that I did, it was because transforms weren’t applied and so the mesh in Blender was actually a tiny spec.
Applying transforms in Blender before export might fix the problem.
The problem is that from JME’s perspective, the mesh data is tiny until animations are applied… but the skinning is (by default) done in the shader and so Java code never sees that data. It’s possible to fix this in your code after the model is loaded but it requires turning off hardware skinning and then forcing the meshes to recalculate their bounds.