SkiaSharp multi-threaded drawing

Does someone have a code sample of how to do multithreaded SkiaSharp drawing? I'm trying to achieve that in a PCL, but I've not gotten any further.

What I'm trying to do is:
1. await method X in method A
2. in method X start a new Task which returns a SKImage
3. in method X create (and dispose when done) SKSurface
4. draw to the Canvas of created SKSurface
5. return SKSurface.Canvas.Snapshot
6. in method A draw the returned SKImage to the original SKCanvasView's Surface.Canvas
7. dispose the SKImage
8. dispose original SKCanvasView's Surface.Canvas

But at step 6 I get the following exception:

[Mono] Found as 'sk_canvas_draw_image'.
[mono-rt] Stacktrace:
[mono-rt] 
[mono-rt]   at <unknown> <0xffffffff>
[mono-rt]   at (wrapper managed-to-native) SkiaSharp.SkiaApi.sk_canvas_draw_image (intptr,intptr,single,single,intptr) <0x0004f>
[mono-rt]   at SkiaSharp.SKCanvas.DrawImage (SkiaSharp.SKImage,single,single,SkiaSharp.SKPaint) [0x00037] in <8e4c06e066264a27bdda5f7ce87d3a90>:0
[mono-rt]   at MyView/<OnDrawGraph>d__6.MoveNext () [0x00177] in /.../Views/MyView.xaml.cs:72
[mono-rt]   at System.Runtime.CompilerServices.AsyncMethodBuilderCore/MoveNextRunner.InvokeMoveNext (object) [0x00006] in <3fd174ff54b146228c505f23cf75ce71>:0
[mono-rt]   at System.Threading.ExecutionContext.RunInternal (System.Threading.ExecutionContext,System.Threading.ContextCallback,object,bool) [0x00073] in <3fd174ff54b146228c505f23cf75ce71>:0
[mono-rt]   at System.Threading.ExecutionContext.Run (System.Threading.ExecutionContext,System.Threading.ContextCallback,object,bool) [0x00004] in <3fd174ff54b146228c505f23cf75ce71>:0
[mono-rt]   at System.Runtime.CompilerServices.AsyncMethodBuilderCore/MoveNextRunner.Run () [0x00032] in <3fd174ff54b146228c505f23cf75ce71>:0
[mono-rt]   at System.Threading.Tasks.AwaitTaskContinuation.InvokeAction (object) [0x00006] in <3fd174ff54b146228c505f23cf75ce71>:0
[mono-rt]   at System.Threading.Tasks.AwaitTaskContinuation.RunCallback (System.Threading.ContextCallback,object,System.Threading.Tasks.Task&) [0x00013] in <3fd174ff54b146228c505f23cf75ce71>:0
[mono-rt]   at System.Threading.Tasks.SynchronizationContextAwaitTaskContinuation.Run (System.Threading.Tasks.Task,bool) [0x00021] in <3fd174ff54b146228c505f23cf75ce71>:0
[mono-rt]   at System.Threading.Tasks.Task.FinishContinuations () [0x000b5] in <3fd174ff54b146228c505f23cf75ce71>:0
[mono-rt]   at System.Threading.Tasks.Task.FinishStageThree () [0x0003d] in <3fd174ff54b146228c505f23cf75ce71>:0
[mono-rt]   at System.Threading.Tasks.Task`1<TResult_REF>.TrySetResult (TResult_REF) [0x00050] in <3fd174ff54b146228c505f23cf75ce71>:0
[mono-rt]   at System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<TResult_REF>.SetResult (TResult_REF) [0x00040] in <3fd174ff54b146228c505f23cf75ce71>:0

The original code:

async void OnDrawGraph(object sender, SKPaintSurfaceEventArgs e)
{
    var canvasWidth = e.Info.Width;
    var canvasHeight = e.Info.Height;

    using (var theCanvas = e.Surface.Canvas)
    {
        theCanvas.Clear(MyArgs.GraphBackgroundColor.ToSKColor());

        using (var axesImage = await DrawAxes(args, theCanvas))
        {
            theCanvas.DrawImage(axesImage, 0, 0);
        }

        theCanvas.Flush();
    }
}

// theCanvas is from old code and is not used anymore (gonna remove it if multithreading works)
async Task<SKImage> DrawAxes(MyArgs args, SKCanvas theCanvas)
        {
    return await Task.Run(() =>
    {
        using (var myCanvas = SKSurface.Create((int)args.GraphWidth, (int)args.GraphHeight, SKImageInfo.PlatformColorType, SKAlphaType.Premul))
        using (SKPaint paint = new SKPaint())
        {
            int numberOfAxes = ...;
            float axisYPosition = ...;

            var axis = new Axis
            {
                Args = args,
                YPosition = axisYPosition,
                HeaderText = "1",
                IsBaseXAxis = (i == 0)
            };

            axis.Draw(paint, myCanvas.Canvas);
        }

        return myCanvas.Snapshot();
    });
}

Any help would be appreciated, as I'm highly stuck :-)