This is very old, but I also struggled with this bug.

The following eventually worked: Set minimum-scale=1;

 <meta name="viewport" content="width=device-width, initial-scale=1, minimum-scale=1" />

renderer.setSize( window.innerWidth, window.innerHeight ) somehow messes up the innerWidth and innerHeight. This also happens if the 3rd argument is false (updateStyle) and you set renderer.domElement styles manually.

setting minimum-scale=1 prevents scaling to accommodate the canvas.