On windows:

1. Open the attached 'blendShapesProblem' scene.
2. select the 'Firetruck_elephant_04_png' object, in the fire engine hierarchy
3. Skinned mesh renderer, open the 'blend shapes' group arrow, and change the 'squash' parameter from 0 to something else.
- the mesh appears in the game view. Same for the other blend shape objects in the scene.
- If I set the values back to 0, they don't disappear.

Play the scene and they are invisible again.(but the user said that on Mac: Hitting play doesn't help - you should to reopen scene)

See user's description