Solved - import weight painting from blender problem

What’s going on? Please help.
It’s a bird wing and I’m trying to make the primary flight feathers fan out using a weight gradient. It moves fine in Blender, but in unity half the feathers rotate fully and half of them don’t rotate at all. The weights are all or nothing.
Here is a video of it

I’m fine with skinning arms and legs.
Is it because the bones are outside the mesh?

Here’s the Blend file

Blender 2.79
FBX 7.4 binary
Unity 2019.2.0f1


In Unity Edit - Project Settings - Quality - Other - Skin Weights = 2