Basic JsonConvert.SerializeObject() stopped working on IoT Core

Question

The follow code is a simplistic example of the issue that I'm having. This was working fine on IoT Core but now when debugging it jumps over var personJson line and never sets a value. I've tested this same code in a blank UWP app and ran it fine on my desktop.

I'm running Windows IoT Core v.10.0.16299.371 on a Raspberry Pi3 B. I'm sure the code was working on v.10.0.16299.309.

Anyone have an idea of what may be happening?

public sealed class StartupTask : IBackgroundTask
{
    private BackgroundTaskDeferral deferral;

    public void Run(IBackgroundTaskInstance taskInstance)
    {
        deferral = taskInstance.GetDeferral();
        LoadPerson();
    }

    private void LoadPerson()
    {
        Person person = new Person();

        person.firstName = "John";
        person.lastName = "Doe";
        person.age = 21;

        var personJson = JsonConvert.SerializeObject(person, Formatting.Indented);
    }
}

public sealed class Person
{
    public string firstName { get; set; }
    public string lastName { get; set; }
    public int age { get; set; }
}