The player can move grabbed parts on their local z-axis using the touchpad. The behavior works as expected, and consistently, in the editor. But the behavior breaks in the build. Sometimes the object travels up and down, or sometimes diagonally.
Edit: Just tested the feature in Unity 2018.2.15f1 and the behavior was consistent between editor and build. Not sure what caused the issue in Unity 2017, but I can call this 'solved' for now.