A parent object is gone (not visible) after Resizing child's RectTransform, parent's RectTransform and child's RectTransform (again) int the Scene view. It stays in Hierarchy however it's not visible in the Scene.

Steps to reproduce:
1. Create an image (default size of 100x100 is fine)
2. Add another image as a child of the first image. Set the child to a smaller size (50x50 works, mainly just so you can see the parent rect box)
3. Select the child in the Hierarchy
4. Select the resizing tool (the one that lets you adjust the edges of the rect)
5. While the child is selected, grab the parent rect and try to adjust it. Let go and it will "snap" back, however it doesn't return to it's size. It seems to vanish and you'll start getting "Look rotation vieweing vector is zero" in the console as you move your mouse over the parent/child group.
6. Now adjust the child size.

Result: The parent image will vanish.

Workaround: Select the parent in the hierarchy and then change it's width or height in the inspector and it will reappear, thus fixing the issue.

Reproduced with: 2017.1.0b1. 5.6.0f3, 5.5.3f1.

Note: a message is spammed to Console:
Look rotation viewing vector is zero
UnityEngine.Quaternion:LookRotation(Vector3, Vector3)
UnityEditorInternal.Slider2D:CalcDeltaAlongDirections(Int32, Vector3, Vector3, Vector3, Vector3, Vector3, Single, CapFunction, Vector2, Boolean) (at /Users/builduser/buildslave/unity/build/Editor/Mono/EditorHandles/Slider2D.cs:290)
UnityEditorInternal.Slider2D:Do(Int32, Vector3, Vector3, Vector3, Vector3, Vector3, Single, CapFunction, Vector2, Boolean) (at /Users/builduser/buildslave/unity/build/Editor/Mono/EditorHandles/Slider2D.cs:124)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)