QualitySettings.GetQualityLevel doesn't seem to return reliable values

Since other people have run into the same problem, I'm assuming there's a bug that causes QualitySettings.GetQualityLevel to return zero regardless of the current setting, at least in some circumstances. That seems to happen for me in the build (but not in the editor), and other people have reported the same problem, such as in this post: https://answers.unity.com/questions/1037255/get-current-quality-settings.html

I'm using 5.0.1.

 

Is updating to a newer Unity version an option for you? 5.x is unsupported already and perhaps it's fixed in 2017.4 LTS.

 

I can't upgrade in the middle of a project.

 

Further testing found that the problem only happens on some machines, which seems very strange given that it should just be reading from a Unity variable rather than doing something that's platform-specific. But when it happens, it makes the game look terrible by defaulting to the lowest setting.