If an animation key doesn't explicity define the scale value, it is set to (1, 1, 1) instead of (0, 0, 0).

utils/exporters/blender/addons/io_three/exporter/api/animation.py

@@ -515,7 +515,7 @@ def _scale(bone, frame, action, armature_matrix):
     :param armature_matrix:
 
     """
-    scale = mathutils.Vector((0.0, 0.0, 0.0))
+    scale = mathutils.Vector((1.0, 1.0, 1.0))
 
     change = False