To reproduce:
1. Open the "Scene" scene in the user-provided project
2. Expand the "Layout Group" in the Hierarchy
3. Disable and re-enable one of the child game objects

Desired outcome: Child game objects are positioned the same way they were before disabling one of them.
Actual result: The child game objects that were not disabled do not update their positions and the re-enabled one appears on the side.

Workaround: Disable and re-enable Horizontal Layout Group component for the parent Game Object.

Note: The same issue applies to the Vertical Layout Group as well.

Reproduced with 2017.1.0a3, 2017.1.0p3, 2017.2.0a1, 2017.2.0b6, 2017.3.0a1, 2017.3.0a3
Not reproduced with 5.5.1f1, 5.5.4p2, 5.6.3f1, 2017.1.0a1, 2017.1.0a2
Regression introduced in 2017.1.0a3