MarshalDirectiveException in Unity when marshalling int[] to SafeArray

Question

Marshalling int[] to SafeArray seems to behave differently in Unity and in a standalone .NET application.

I have a COM dll that defines an interface

[ComImport]
public interface Calibration
{
    [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
    [return: MarshalAs(UnmanagedType.SafeArray, SafeArraySubType = VarEnum.VT_INT)]
    Array getInputKey();
}

In my C# script, either in Unity or in a standalone .NET application, I created my class that inherits from Calibration

public class MyCalibration : Calibration
{
    private static readonly int[] _inputs = new[] { 0 };

    public void doSomethingElse() 
    {
        // Something
    }

    public Array getInputKey()
    {
        return _inputs;
    }
}

Another COM object has a method

[MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
void setCalibrationInterface([MarshalAs(UnmanagedType.Interface), In] Calibration ical);

I created an instance of MyCalibration and used it as the argument to the setCalibrationInterface method.

var myCal = new MyCalibration();
util.setCalibrationInterface(myCal);

The doSomethingElse() gets called without a problem. However in Unity I got the following exception when getInputKey() gets called in the Unity Console:

MarshalDirectiveException: The type 'System.Array' layout needs to be Sequential or Explicit
(wrapper native-to-managed) SREYELINKLib.ICalibration.getInputKey(intptr,System.Array&)
UnityEngine.<>c:<RegisterUECatcher>b__0_0(Object, UnhandledExceptionEventArgs)

Any ideas how to fix this?