To reproduce:
1. Open attached project
2. Open TestScene
3. Enter play mode
4. Wait for Actual Pos to become a static number
5. Start clicking the buttons to change target position
6. Notice the object does not change it's position
Expected result: The joint continues to react and update it's position to the Target position as usual
Actual result: It's frozen

Note: Any action upon the object returns the behaviour to normal. My guess is that changing target position does not wake up a sleeping object.

GIF: https://gyazo.com/af38b69f881b0d4c975a7a7e5f3ae453