How to reproduce:
1. Open attached Unity project
2. Select CubeBlend in the Hierarchy window
3. In the Inspector window, click "Link SMR"
4. Click "Create/Link"
5. Enter a unique blendshape name
6. Click "Duplicate"
7. Adjust created slider - vertices move
8. Repeat 5 and 6 steps - vertices don't move

Expected result: Sliders should move vertices.
Actual result: Sliders, created after moving created sliders, has no effect on vertex movement.

Reproduced with: 2019.2.8f1, 2019.3.0b6, 2020.1.0a8.

Notes:
- User mentioned that this is a regression from 2017 or 2018 Unity version. Can't test it. The project doesn't work correctly in 2017.4 Unity version.
- Can't test on 2018.4. Project crashes on opening.