We were able to reproduce the problem.
Yes, this is because the size is not 256 * N.
Thank you for reporting the problem.

We will try to fix it.
But this is perhaps the most deep and difficult problem that I ever seen (in Online Maps), and I do not know how long it will take.

I tried playing around with width/height of map. It was set to 1920x1920. I tried setting it to 256x256 and it worked, so I thought it might be a resolution issue. Then I tried 512, then 1024, and they worked. I tried 1080, and it was wrong again. Then I tried 2048, and it was fine (albeit a bit slow).

It seems to only work when it's a power of 2. Is it because the tiling is set in powers of 2?

Possible there is not enough accuracy with such a small line thickness.
Please show your Online Maps settings and GameObject Transform.
We will try to reproduce and fix the problem.

I've had to scale my markers down to .005f, as in the HTC Vive, they come out huuuuuge otherwise. I'm not sure if this would affect it, and they would otherwise be in the correct place?

I set the line weight to .001f, as again, it just covers the entire map otherwise.

My code's fairly simple:

foreach (double[] coord in geoms)
        {
            Vector2 pos = new Vector2((float)coord[0], (float)coord[1]);
            OnlineMapsMarker3D marker3D = control.AddMarker3D(pos,spawnPrefab);
            marker3D.scale = 0.005f;
            //positions.Add(pos);
        }
        double[] positions = geoms.SelectMany(i => i).ToArray();
        OnlineMapsDrawingLine line = new OnlineMapsDrawingLine(positions, Color.green, .001f);
        OnlineMaps.instance.AddDrawingElement(line);

Any idea?