Reproduction steps:
Example 1:
1. Open the attached project
2. Open the "bug report scene"
3. Select the "text" gameobject in the hierarchy

Result: "text" has a Content Size Fitter component with Unconstrained horizontal fit, but you cannot see half the text

Example 2:
1. Open the attached project
2. Open the "bug report scene"
3. Select the "Content" gameobject in the hierarchy
4. Type anything into it

Result: preferred Width doesn't change, but height does.

Reproducible on: 5.5.0b11, 5.5.0f1
Not reproducible on: 5.3.7p1, 5.4.2p4