To reproduce:

1. Download attached project "IOSCONTROL.zip" and open in Unity
2. Open "Title" scene
3. On Hierarchy expand "Canvas" game object
4. Expand "New game button" game object
5. Select "Text" game object
6. On the "Inspector" window, in the "Text (Script)" try to write some long text (in example: Hellooooooooooooooo)

Expected result: Text resizes accordingly
Actual result: Text doesn't resizes

Note: If you go to "fonts" folder, select "Asset.ttf" file and change "Character" type to "Dynamic", then "Best Fit" applies to the Text component, but font resolution becomes blurred

Reproduced on Unity 5.5.3.f1, 5.6.0f3 and 2017.1.0a6
Could not check for regression in 5.4.x, because files can not load

Video is in "Best Fit is broken.rar" file