Nativize BP Package fails when using Sub Anim Instance with exposed variables

When using exposed variables on Sub Anim Instance nodes, packaging with nativize blueprints fails

Tested on:
4.15 - 3450819
4.16 - 3466753
4.17 - 3502710

1. Download the attached project
2. File>Package Project>Windows>64 bit
3. Choose a folder and package

Result: Package fails
Expected: Packages successfully

1. Create a Third Person Test Project
2. Create two AnimBPs (A Parent and Sub)
3. In the Sub Anim BP, create a blend with "ThirdPersonWalk" and a "Sub-Graph Input" node. (See SubAnimGraph screenshot attached)
4. Promote the alpha to a variable (make the variable exposed)
5. In the Parent AnimBP, set up a "Sub Anim Instance" node and plug in the Sub AnimBP
6. Expose the float variable
7. Promote that to a variable and make the default 1
8. Plug in Local Ref Pose to the In Pose (See attached ParantAnimGraph screenshot)
9. Apply the Parent AnimBP to the Third Person Character Skeletal Mesh
10. Edit>Project Settings> Packaging
11. Set Nativize Blueprints to "Inclusive"
12. File>Package>Windows>Win64
13. Select Folder and package

Result: Package Fails
Expected: Packages Successfully